Griefer

A griefer or bad-faith player is a player in a multiplayer video game who deliberately and intentionally irritates and harasses other players within the game (trolling), by using aspects of the game in unintended ways in order to destroy something another player made or built, or stealing something, such as items or loot, when that is not the primary objective.[1] 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. If a bad-faith player is attempting to gain a strategic advantage, it could be considered cheating.