1) MUD terminology 2) Video game gameplay term 
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 cann...
(slang) A user who's goal it to irritate and harass other players, rather than in pursuit of game objectives.
Irritating player
A player of an online game who harasses other players.
A player who looks to be destroying other peoples work on purpose, this causing havoc around the world and can be rather annoying. ~ Keyofdoor ~