I have a friend who is in London and is using Citibank to transfer over $100,000 to his account in usa. He is telling me there is a tax fee and bank fee that adds to 4000 in pounds. Does this sound like too much??

Sounds very suspect.
Are they asking YOU to pay this "fee" ?

Yes, he is asking for help. Does sound like allot to me.

Honestly sounds like a complete SCAM..
Do you actually know this person in real life and have you met them in the flesh.

Your exactly right. This is what I suspected. Thanks for your help.

And, even if you do know and have met the person-- are you sure that it is that person that is making the request to you? Especially, if this is an email or other electronic communication, call and speak to the person. They may not even be involved in any such arrangement.