A 'ninja' fore me is related to:
anyone who chooses Need on an item roll that dont suits his class or maybe he has an equal or better item and wants that for selling or some other thing that doesnt urgently fills the need of the actual char.
That is just being a ***** and a lootwhore. I have left flashpoints for this. And the item was not even for me.
The term is ninja is to take something from someone while using a distraction.
i.e. taking a static loot chest from someone while they are fighting the mobs that are protecting it (mobs are distraction).
i.e. Capping a point while the enemy is fighting your friendly forces.
Ninja Cap, Ninja Loot, etc.