a.) Slang term for the fatty deposits on a person's buttocks. Asses come in various sizes, ranging from 0 (none to speak of) to 10 (morbidly obese), with the average being somewhere around 5 to 7.
b.) A donkey.
c.) An obnoxious or egocentric person.
a.) I have no ass, so I'm trying to find some padded panties.
b.) That ass may look tame, but he packs a wallop.
c.) Tiffany is such an ass. She talks about herself all the time.
While gaming, other players may either purposefully or accidentally piss you off. The appropriate thing to do is type "ass" for every time you kill such a player.