I'm sure at some point in time we've all seen epic looting nightmares. More than once I've been hoping for a drop in an instance only to have another party member beat me on a need roll. Usually, though it's something they actually do need, at least as much as I do. Sometimes ninja looting is even an accident, but other times it is not.
Avirisa of Mannoroth is a might miffed that she was outrolled for a Commendation of Kael'Thas ... to a Hunter... for PvP. As a tank, she said he was running the instance to acquire that drop. Most responded that this behavior is part of what gives Hunters a bad name in the game (Huntard). Some blamed the original poster for inviting not only a Hunter, but a Night Elf Hunter to the group.
Boxtor of Doomhammer sided with the Hunter since the stamina is good for PvP or even that the Hunter was probably of the impression that the original poster wanted it for PvP as well. Perhaps the Avirisa should have made her loot intentions clear at the beginning of a run. Gagger of Carine believe that looting in this manner is acceptable as loot conventions tend to be loose in pugs.
This one seems like a no-brainer to me. You've got a tank who has been running the instance for a tanking item. It seems that player should get first dibs. The immediate needs of the players in their roles in the group takes precedence over gearing extraneous sets. I think that blaming the player's Race or Class is irrelevant. There are ninjas of every race and class.
Have you ever lost out on an item in this way?