1) People who bolt on an elevator before you have a chance to step out.
2) Men who don't hold the door for the ladies or people that don't look back and let a door slam in your face.
3) Car-horns - I'll fight you in a minute if you blow your damn horn at me because I'm not moving fast enough for you.
4) People that don't let you merge into traffic.
I guess I'm all about courtesy...