Griefer

A griefer or bad-faith player is a player in a multiplayer video game who deliberately annoys, disrupts, or trolls others in ways that are not part of the intended gameplay. Griefing is often accomplished by killing other players unnecessarily, destroying player-built structures, or stealing items. A griefer derives pleasure from the act of annoying other users, and as such, is a nuisance in online gaming communities.