I remember I was playing some Halo and i managed to get more ammo for my sniper rifle I'd been carrying the entire game and another guy ran up as soon as I had picked up the ammo. I looked at him a sec and he looked at me. Being generous I picked up a pistol and let him have the sniper rifle. I walked away. He shot me in the back of the head and spent half the ammo shooting randomly until an enemy had finally killed him.