People who can't follow simply instructions. Specifically on public transport. Like "stand clear of the doors" actually means stand clear of them, it does not mean shove bodyparts between them so you can get on and slow everyone else down because you got up late, it does not mean stand so close that the things won't close because you're too selfish to just get off and wait for a less crowded train.
Or those who ignore the "Please allow passengers off" messages. I hate those people, because I always wait and allow people off, and then because other people shove their way on rudely, they get seats, and in extreme cases, get on at all, when I don't.
Rudeness of any form annoys me, as does selfishness. Wish more people would understand that the world doesn't revolve around them (strange coming from me, I realise, but I've learnt my lesson).