Habafa- a word of excitement, horror, confusion, or any exclamation really.
Used when they can't think of a way to express the feeling they're experiencing, or they just want to use something unique. It is more often used online, as it's quite difficult to pronounce habafa.
This term is sometimes used to denote that a user is present but essentially AFK (away from keyboard). This usually applies when somebody is playing a game, watching a movie, or doing something else that prevents them from being able to receive and reply to some form of messages within a reasonable period of time.
IRC:
User: Hey guys, I'll have to catch you later.
<<User changes his/her nickname to User|HBAFK.>>