What is "griefer"

n. (context online gaming English) One who grief#Verb: a player who plays a game primarily to reduce other players’ enjoyment of it.

A griefer is a player in a multiplayer video game who deliberately irritates and harasses other players within the game, using aspects of the game in unintended ways. A griefer derives pleasure primarily or exclusively from the act of annoying other users, and as such is a particular nuisance in online gaming communities, since griefers often cannot be deterred by penalties related to in-game goals.