Resident Evil Outbreak...one of my funniest moments...
Final stage. Me, Kevin and someone else versus Thanatos-R. The third partner is killed, Kevin and I are at low health. All I have left is a handgun. As Thanatos-R is beating what is left of the life out of Kevin, I steadied my aim, stared him down, and fired right into his zombified behind. Cinima kicks in and I killed him.
This bio-engineered creature of chaos and destruction felled by a butt wound. Laughs were plentiful for me and my friends.
(Also note I do not remember the exact date. So the one submitted is randomized.)