I recall one time, about five years ago, playing SWAT 4 in online CoOp, with three Americans and someone from Asia.
Now, this Asian fella didn't speak or understand English, so while the three Yanks and myself were discussing how to handle the mission, the Asian fella was pretty much left out.
Upon starting the mission, we go ahead and head for the first closed door, which will get us into the building complex itself.
As we reach it, I whip out my peek-under-doors-magic-wand, and go ahead and peek.
I see a couple guys, and start telling the other fellas what is in there, when the Asian dude opens up the door, exposing me to a hail of gunfire, resulting in my immediate and brutal murder, as well as the remaining team being in a very bad way.
Now. Not only did he do this once, but five times (although not at the same door), with the same result.
After that, we just started each mission by blowing his head off. Stopped us from actually completing it properly, but at least we actually got to play the game.