Delayed failure
At the end of a level, point your crosshairs at your teammate and set your weapon to full automatic. When the screen starts to go black begin shooting your teammate. When he dies the screen will still be black but the game will not return to the main screen immediately. It will stay black but you will still be able to move around and shoot for about a minute. The game will then return to the main screen and say that you failed because you shot your teammate.