My biggest is rudeness/inconsiderateness.
Consider other people's feelings before you do/don't do something. Fucking idiots. I'd rather someone consciously make a decision I don't like AFTER considering my feelings than someone who just doesn't think about it, doesn't cross his/her mind. That shit is aggravating.
Also, if you're going to do something, DO IT. Either that or you'd better have goddamned good reason for not doing it, because someone is EXPECTING you to follow through.
Oh, another one...when you say "thank you" to someone for something (i.e. a waiter after he brings your food), and that person doesn't say ANYTHING. Fucking acknowledge the fact that I'm speaking, you braindead motherfucker. I said something. Acknowledge it in some fashion.