Is it normal for my teenager to walk in the house or room that I'm in and not greet me?

While it is probably "normal" (because my kids did the same thing), it's not (in my opinion as a mom and grandmother) polite. It's downright rude. It was not because I didn't teach my children manners, but I think as with most teenagers, it's just their way of showing their control. I don't know if your child is a young teenager or an older teenager, but I know that they go through their stages. This is just my opinion based on my past experiences. I would usually make a joking remark to them such as... "I'm fine thank you and yourself?". If it truly bothers you, speak with your teen about manners and being polite. Good luck.

Very very normal.
Teens are struggling with being children about to be adults, and usually feel a need to pretend that they are on their own. Let the little irritations slide and concentrate on the important ones. Try to joke about it; maybe say 'too old to say hi, but not too old to ask for one of my homemade brownies (allowance, cell phone, new sweatshirt, drive to mall)?'

I'm a fan of the dinner discussion about anything that needs addressing, with the rule that it be kept calm. Teens do need to understand that you are legally liable for them, that they are being supported and that support takes money, and must accept that certain demands go with being under 18. They should have their ethics and morals pretty much formed, learned by example from you. But money is often the crux of many problems and they could sit in on monthly bill paying and plans for spending, if only to learn finance management as young adults.

I say normal. I'm not too very far out of my teens (I'm 26 ) and remember as a teenager, I didn't notice anything except what was on my mind. If I got home and was hungry, the fridge was the only thing in the house! Lol! I wouldn't take it personally if I were you. Just start, " Hey kid. Howzit?" and I'm pretty sure you'll get greeted back. :-)