In Modern Warfare 2 a person in 3rd person cage match who will trick you into letting them get a certain amount of headshots and then leave the match unexpectedly after getting their wanted number of headshots.
Gamer#1:"hey lets do headshots."
Gamer#2:"okay sounds good to me."
(19 headshots later)
Gamer#1: (Leaves game without notice after getting 19 headshots)
Gamer#2:"What the hell freaking Headshot whore!!"