My friend introduced me to a friend of hers. We were over at his house. He had a roommate. The roommate seemed like a nice guy. He went and changed from pants and long sleeves into shorts and a short sleeve shirt. We automatically saw cuts all over his body. He started talking about how he kept seeing things... evil things such as demons. He suddenly switched back to being calm and told us some more funny stories. Then he told us a sad story of something that happened to him. The next thing he said was "hold on, i have to forget this." Suddenly he lifted his hand up, made a fist, then punched himself in the temple. We panicked, he went limp, wasn't responding but was still breathing. Then he appeared to be having a seizure. Then after only one minute, he sat up and didn't say anything. His friend said (we'll call him mike) "Mike, are you ok? Are you ok Mike." Mike turned and looked and said "Yes. My name's Mike" he just kept repeating that. Me and my friend left. We agreed to go back over because we thought he was going to be gone and it was supposed to only be my friends friend there. Mike showed up again. He seemed really calm, friendly, and nice. He started just telling us more stories. Then out of nowhere asked if me or my friend would carve devil into his back with a knife because he couldn't reach. We said no and he even offered us $100 to do it. Again we said no. Then he dropped it and started telling us another story. I felt bad for being rude to him and I asked him why he cut himself. He said he was told to. He just kept telling me to go to church, everything will be fine if you go to church. He seems like a nice guy but he definitely is not right. Is there any reason for me to be afraid of him harming me? He found out some things about me such as where my dad works, where I work, and what religion I am. Should I be worried for my family? Please help

Just get out of there and don't ever go back!! Its too dangerous for you. Stay away!

Stay far far away. If he's listening to voices telling him to cut himself, there's no knowing if those voices are going to tell him to come after you next. Creepy! Don't go over there anymore. Whether you believe he will be there.

This guy has mental health problems which should by my guess have already have been diagnosed. Maybe he was not taking his medication or the medication needs to be looked at.
It is a hard question to answer as I do not personally know the guy.
For those who do not understand it is a medical illness can be very afraid.
Have you spoken to your friend about this friend they have over?

Demonic possession is often the term used to describe the control over a human form by a demon. Descriptions of demonic possessions often include: erased memories or personalities, convulsions, “fits” and fainting as if one were dying.[1] Unlike in channeling or other forms of possession, the subject has no control over the possessing entity and so it will persist until forced to leave the victim, usually through a form of exorcism. Other descriptions include access to hidden knowledge and foreign languages, drastic changes in vocal intonation and facial structure, sudden appearance of injury (scratches, bite marks) or lesions, and superhuman strength.

Many cultures and religions contain some concept of demonic possession, but the details vary considerably. The Roma people believe that demons can also possess animals, plants, deceased persons or inanimate objects.

The oldest references to demonic possession are from the Sumerians, who believed that all diseases of the body and mind were caused by "sickness demons" called gidim or gid-dim [2]. The priests who practiced exorcisms in these nations were called ashipu (sorcerer) as opposed to an asu (physician) who applied bandages and salves[3]. Many cuneiform tablets contain prayers to certain gods asking for protection from demons, while others ask the gods to expel the demons that have invaded their bodies.

Most illustrations portray these spirits as small, sadistic-looking or tormented-looking beings with a human likeness. Demons are often referenced as familiars. Witches would provide shelter and nourishment via the witches' teat in exchange for the valuable services of familiars.[4]

Shamanic cultures also believe in demon possession and shamans perform exorcisms too; in these cultures often diseases are attributed to the presence of a vengeful spirit or (loosely termed) demon in the body of the patient. These spirits are more often the spectres of animals or people wronged by the bearer, the exorcism rites usually consisting of respectful offerings or sacrificial offerings.

Source - Demonic possession - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Demonic_possession)

Well when we were over there, my friend's friend said that he has known the guy almost his whole life and he said that he is a really nice guy but is "different" is how he worded it. As far as we know, he is not on any medication. I do have every intention of avoiding him but his friend says that "Mike" is starting to like me... not a very comforting thought. Has anyone even heard of anything like this with the whole demon thing and the slicing thing? Is there a certain mental illness that he has?

He's schizophrenic, sounds like -- maybe even psychotic.

Being in some kind of cult also springs to mind here to!

I work with this area so it is not unusual to me.

At first thought I would say the guy suffers from schizophrenia -

A person diagnosed with schizophrenia may demonstrate auditory hallucinations, delusions, and disorganized and unusual thinking and speech; this may range from loss of train of thought and subject flow, with sentences only loosely connected in meaning, to incoherence, known as word salad, in severe cases. Social isolation commonly occurs for a variety of reasons. Impairment in social cognition is associated with schizophrenia, as are symptoms of paranoia from delusions and hallucinations, and the negative symptoms of avolition (apathy or lack of motivation). In one uncommon subtype, the person may be largely mute, remain motionless in bizarre postures, or exhibit purposeless agitation; these are signs of catatonia. No one sign is diagnostic of schizophrenia, and all can occur in other medical and psychiatric conditions.[4] The current classification of psychoses holds that symptoms need to have been present for at least one month in a period of at least six months of disturbed functioning. A schizophrenia-like psychosis of shorter duration is termed a schizophreniform disorder.[4]

Schizophrenia is often described in terms of positive and negative (or deficit) symptoms.[15] The term positive symptoms refers to symptoms that most individuals do not normally experience. They include delusions, auditory hallucinations, and thought disorder, and are typically regarded as manifestations of psychosis. Negative symptoms are so-named because they are considered to be the loss or absence of normal traits or abilities, and include features such as flat or blunted affect and emotion, poverty of speech (alogia), inability to experience pleasure (anhedonia), lack of desire to form relationships (asociality), and lack of motivation (avolition). Research suggests that negative symptoms contribute more to poor quality of life, functional disability, and the burden on others than do positive symptoms.[16]

Despite the appearance of blunted affect, recent studies indicate that there is often a normal or even heightened level of emotionality in schizophrenia, especially in response to stressful or negative events.[17] A third symptom grouping, the disorganization syndrome, is commonly described, and includes chaotic speech, thought, and behavior. There is evidence for a number of other symptom classifications.[18]

Psychotic symptoms may be present with several other psychiatric illnesses, including bipolar disorder,[21] borderline personality disorder,[22] schizoaffective disorder, drug intoxication, either intoxicated or abstinent drug-induced psychosis, and schizophreniform disorder. Schizophrenia is complicated with obsessive-compulsive disorder (OCD) considerably more often than could be explained by pure chance, although it can be difficult to distinguish compulsions that represent OCD from the delusions characteristic of the schizophrenia.[23]

A more general medical and neurological examination may be needed to rule out medical illnesses which may rarely produce psychotic schizophrenia-like symptoms,[4] such as metabolic disturbance, systemic infection, syphilis, HIV infection, epilepsy, and brain lesions. It may be necessary to rule out a delirium, which can be distinguished by visual hallucinations, acute onset and fluctuating level of consciousness, and indicates an underlying medical illness. Investigations are not generally repeated for relapse unless there is a specific medical indication or possible adverse effects from antipsychotic medication.

"Schizophrenia" does not mean dual personality, despite the etymology of the word (Greek σχίζω = "I split").

hoping this helps you understand a little more if indeed this is what the guy suffers with -

source - Schizophrenia - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Schizophrenia#Signs_and_symptoms)

He's schizophrenic, sounds like -- maybe even psychotic.

Psychosis is not a condition in itself. It is a symptom of other conditions. The most common cause of psychosis is a mental health condition such as schizophrenia or bipolar disorder (manic depression).

Trouble is, schizophrenics and those with a psychosis are usually non-compliant with drug-taking. Even if he is prescribed a med or two, he may take it for a while, but as soon as he feels better or more normal, he will stop and then within a couple of weeks (once the meds wear off) will revert to his former behavior.

I suggest you stay away from this fellow.

Like I said before, stay far far away. Mike can like you all he wants far far away. Don't give him your number, email, anything. Don't add him to Facebook, myspace, or anywhere. Make sure your friends know not to give him any information about you.

Psychosis is a term that is used to describe a mental condition where somebody is unable to distinguish between reality and their imagination.

People who are experiencing psychosis are referred to as psychotic. People with psychosis often experience:

Hallucinations - where you hear or see things that are not there, and
Delusions - where you believe things that are untrue.

Psychosis is not a condition in itself. It is a symptom of other conditions. The most common cause of psychosis is a mental health condition such as schizophrenia or bipolar disorder (manic depression).

Psychosis can also be triggered by physical conditions, such as Parkinson's disease, or as a result of drug or alcohol abuse.

How long someone will experience a psychotic state of mind, known as a psychotic episode, will depend on the underlying causes. Drug- or alcohol-induced psychosis many only last for a few days. However, psychosis that is caused by schizophrenia or bipolar disorder may last indefinitely unless it's treated.

How common is psychosis?
Psychosis is more common that most people realise. It is estimated that one in every 200 people in the UK has experienced psychosis. Some people will only experience one psychotic episode, while others may experience a number of episodes throughout their life.

Treating psychosis
Prompt treatment is recommended for psychosis because studies suggest that the earlier the condition is treated, the better the long-term results tend to be. In the short term, medicines are used to treat the symptoms of psychosis to make sure that the person is no longer a danger to themselves or to others. The long-term treatment will depend on the underlying causes.

'Psychosis' is not the same as 'psychopath'
The term psychosis should not be confused with the term psychopath. The two conditions are very different.

Someone with psychosis has an acute condition that, if treated, can often lead to a full recovery. A psychopath is someone who has an incurable anti-social personality disorder, which means that they lack the capacity for empathy, are manipulative and often have a total disregard for the consequences of their actions.

Unlike people with psychosis, people with anti-social personality disorder can appear to act in a rational manner.

Source - Psychosis - Introduction (http://www.nhs.uk/Conditions/Psychosis/Pages/Introduction.aspx)

He definitely did not lack motivation. Just to give you an idea of what he looks like, he is about 6'5, has VERY large shoulders, can bench 500 pounds, and from what his friend says, he hardly sleeps and goes running every night. He is not a small guy. Another thing was that we could all be sitting and watching a movie and randomly he would jump up and leave and then a few minutes later, just casually come back over and sit down... next to me always. That is very helpful, what you were saying. I think there is a large possibility that he could be suffering from schizophrenia...

He definitely did not lack motivation. Just to give you an idea of what he looks like, he is about 6'5, has VERY large shoulders, can bench 500 pounds, and from what his friend says, he hardly sleeps and goes running every night. He is not a small guy. Another thing was that we could all be sitting and watching a movie and randomly he would jump up and leave and then a few minutes later, just casually come back over and sit down... next to me always. That is very helpful, what you were saying. I think there is a large possibility that he could be suffering from schizophrenia...
That was my schizophrenic/bipolar uncle's behavior -- the movement thing. If a Cubs player made an out, my uncle would leap up and turn off the TV (pre-remote days), even though the rest of us were also watching, and then would sit on the front porch and smoke a cigarette. We'd turn the game back on. After the cig was finished, he would come back into the house and continue watching the game like nothing had happened.

he would come back into the house and continue watching the game like nothing had happened.

That's like what I was talking about when I said he hit himself in the temple and after that whole thing of us freaking out and trying to talk to him, he went back to telling stories and watching TV like there was nothing wrong.

One of our library patrons is an unmedicated schizophrenic who likes to give "Christian hugs" (if he can get away with it, usually can't) and speaks in word salads (all the words are real, but his sentences make no sense). Much of the time, he is a really nice and agreeable guy.

He definitely sounds like he has a demonic spirit and they do tend to be diagnosed with schizophrenia.
How is he finding out stuff about you? Is your friends friend telling him?

I would stay clear, except:

Speak to his friend, and advise him that you do not feel comfortable around him after seeing his behaivour, and ask him to contact the man's parents if he hasn't already.

If he is not on medication, or regularly seeing a physician or psychiatrist of some sort, maybe his parents are not aware. He needs to get checked out before he kills or seriously injures himself.

You don't say how old he is, if he's a student, or working. None of us can make a diagnosis, particularly with knowing so little, but clearly he needs help.

Regardless of what his personal circumstances are, I think it's a shame, and I feel sorry for him that nobody is really helping.

Maybe a phone call from his room mate to his parents could make all the difference.

I don't think trying to diagnose his condition is helpful at all, but it is very clear that he's mentally very unwell.

I agree with Jake that someone has to do something, or otherwise there could be unfortunate and tragic circumstances. See if his roommate can contact his parents - I would be very concerned about living with this guy, given what you've described.

Don't go back there again. He's too unpredictable.