Nearly all forced interaction with people I do not know irritates me to some degree. It's not that I can't get along with others, but I don't always want to.
Most classic literature.
People that type less than 100 WPM. It only really bothers me when I'm watching them do something or waiting for them. It's like watching old people leaving a restaurant: slide out of the booth, hobble to your feet, help your old friends up, look around to make sure you haven't knocked anyone over yet, pick your things up from the booth, look around again, make sure you have your hat, start walking, eventually make it to a door way, stop to make sure there are people behind you, don't let them around to open the door for you, struggle with the push/pull debacle, open the door... I guess add old people leaving restaurants to the list, and add murder being illegal if there are two sets of doors at said restaurant. But people typing less than 100 WPM is that level of pain to witness for me, I just want to do it for them.
People that compare dance games to dancing.
Religion.