My list could be endless. Current annoyances are:
People who don't indicate until they are turning a corner.
Reading 'pack up' instead of 'packed lunch'.
People who drive 10m under the speed limit - where I live there are a ridiculous number of people that drive everywhere at 20mph.
People that spend longer telling you what they want to do when they could do it themselves in half the time it took them to explain. I used to have a boss that would phone me and ask me to ring someone, when he could have just rung them instead 
People that tap, chew, click, squeak their chairs, just generally make loads of noise.
Whistling. Makes me want to punch the person in the face. Hard.
Slow walkers.
People that don't pick their feet up when they walk.
The way some people speak - I don't know what the spoken version of illiterate is but there are some very unfortunate people out there.
People that don't seem to ever wash their cup - there are a couple of people here at work who keep the same cup and the insides are black with tea staining.
People that don't make their children behave properly in public.
Children that scream that earsplitting scream.
Loud people when I'm trying to have a nice meal out and can't concentrate on the menu or what people are saying.
People that smoke nearby when I'm eating.
I should probably stop there 