Yeah, I think the thing about saying hi or not can be kind of confusing. I have always tended not to say 'hi' because I figure people are busy working. I am making more of an effort to say hi, even if I am not sure it's right, because it seems better to be friendly and sociable. I think I prefer this.

The two guys in front may not have anything against you personally. They may just feel like you are interrupting their work or their opportunity to chit-chat with your conversation.

I also think it is possible to have mannerisms that other people don't care for. If you think other people are annoyed with your questions, I would stop asking so many. Maybe volunteer something about yourself instead?