Except for the very young, old or handicapped most people annoy me.
My two hot-buttons are unjustifed rudness and illogical behavior.
Here's an example that combines both into one scenario, last week I was driving home from work. As I was driving down the parkway there was a guy in the left lane going the same speed as the person in the right lane. Basically no one could pass. So I didn't beep, flash my brights or do anything. Instead I calmly pulled behind the person in the right lane and as soon as there was an opening I floored the accelerator and passed the guy in the left lane.
As soon as I passed him he started beeping, flashing his lights and giving me the finger. I just shrugged it off and kept driving. Eventually he disappeared.
Yeah, so in summation those sort of people annoy me.