We had a few good ones in GoW2 both before and after patching it. Some of the classics including wretches running around upside down - as if running on the underside of an invisible table. Our favourite though involved a housemate of mine, playing as Dom on the rig at Landown, finding that the mortar was being held "normally" and allowed him to shoot in the direction faced, but trying to move would turn Dom's body to face that direction, the game simply stretching his arms from any number of painful positions to still hold the mortar...
Oh and the Lady Benezia fight on Mass Effect? Hated it. I failed it dozens of times due to being knocked down next to scenery - Sheppard has to move forward to get up, so if there's scenery in the way he just lies there like some sort of cripple to get slaughtered by the guards.