Rage built up by playing Left 4 Dead 1 or 2, usually occurs from the game not loading on the first, second or tenth time. Sudden connection loss during a really good and close game of Left 4 Dead versus. Or when after waiting a while to finally get a versus game going one of the sides quits when it doesn't win the first level in a crushing victory. And finally horrible connection lag when playing a good game, often leading to poor aim, not being able to help a teammate quickly, or, if playing as infected, accidently spawning in front of the humans with enough time for them to kill you before you can do anything.
It's that Left 4 Dead Rage, it'll get to you.