grabbing loot from a slain monster, chest, etc., that you don't have a right to grab, or that you didn't earn, or that you don't need. Ninja looting is very, very bad form, and - if you do it consistently - can get you labeled by other players as a "ninja looter." Which is a sure way to get yourself black-listed from groups, guilds, and/or raiding parties. Ninja looters often become very lonely players.