1. v. The past tense form of taking an item from a person without their noticing, usually right in their line of vision.
2. Used in the popular game "Halo" for xbox 360 when a player is getting chased down by another from behind, jumps backwards, and assassinates the enemy. (past tense)
Person 1: Where did my gum go?
Person 2: Bob totally ninjad it from you when you were playing basketball with him.
Person 1: Damn it, he is always taking my gum.....
Player 1: How'd you kill that guy when he was chasing you and unloading bullets into your back??
Player 2: I totally ninjad him, he never saw it coming.
Player 1: ohhhhhhh, what a noob....
*tim reaches in his pocket for his phone*
Tim: What the hell, who ninjad my damn phone?
Mike: oh dude I thought you knew I was looking at it like 5 minutes ago.
Tim: How the??
john: dang it she did it again
kate: hahaha he can never ninja me back...i must be too ninja