Battlefield 3's Prone glitch, the fact that you are a moving seal on the ground with your gun pointing upward when you shoot had me rolling.

Another funny glitch was a UFC glitch, when i was in a clinch, and suddenly me and my opponent stopped being in control, and slowly being pulled away from each other, we still had the CLINCH PHYSICS active....

My third is just about the "stuck-in-the-floor" glitch in Lost Planet 2, always a funny way to die in that game.