The act of joining a group and then trying to get as many items as possible, without regard for the well-being of the rest of the group.
I'm a little ninja, short and stout
I take all the loot and I hearthstone out
All the guys on teamspeak scream and shout
I'm the warrior in full devout.
In World of Warcraft, it's customary in many groups to pass on an item when it's being rolled, in order to decide who needs it the most, and then roll again (/random 1-100). A ninja looter will roll on the item, instead of passing, and then may plead ignorance, or may declare that he needs it more than anyone else. Such behavior often results in ejection from the group and blacklisting.