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1.
v. To leave a party without telling anyone you're leaving, so as to disappear- like a ninja.
Dirk dropped a ninja bomb last night, and no one heard peep from him for a week.
by 'noda March 08, 2007
 
2.
To Fart in ones hand and hold it, sneak up behind somebody and throw it in their face.
Robert ninja bombed Chris as he was getting his nipple pinched by the other Chris.
by Yu, Yu, Su September 27, 2006
 
3.
Similar to photobombing, to ninjabomb a picture is to intentionally posing behind other people, peeking over their shoulders, under their arms, and in open spaces in other people's photos, for a later surprise.

The difference between a sneaky photobomb and a ninjabomb lies in that the ninjabomber is dressed like a ninja (in ninja garb).
Drew: "dude, I'm looking through my camera, I don't think I have ANY normal pictures of you from our halloween party last night."
Stephen: "yeah, but you do have over 20 of me ninjabombing."
by aronskelk12 November 02, 2010