People who double-post.
People who drive too slow.
People who leave their car doors half open, or not fully latched. Makes me want to ram my front bumper into the door and close it all the way.
People who seem to have a huge amount of book smarts, but can't figure out simple stuff at work.
People who have to constantly rev the balls off their car when the muffler is shot or disconnected. I almost called the cops on a neighbor for a noise complaint, then went and talked to him and let him know how annoying it was. I've heard him leave, then come back, then leave again, revving to five grand every time. Since I talked to him he's been quiet.
That's all I can think of offhand.