A person who is very subtle or sneaky when it comes to looking at a female's breasts.

Used as a compliment by males and a warning or an insult by females.
Girl1: Bob said that he didn't masturbate. He's so lying.

Girl2: I dunno. Maybe he's telling the truth. I mean, I've never seen him look at a girl's boobs before.

Girl1: That's because he's probably a boob ninja.
by Littleman29 February 25, 2010
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A ninja that is addicted to boobies and possibly cocaine.
Woah, that boob ninja was totally just checking me out.
by The Waffler December 9, 2005
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Boobs you wouldn't really think are big from an "in the shirt" perspective, but when released from captivity they sneak up on you and are huge. Like a ninja
I didn't realize her boobs were that big until she took off her shirt, they were totally big and amazing. I love her ninja boobs.
by Brian Street Team March 24, 2009
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1. Breasts of a small caliber; often found of female ninjas

2. Tightly contained breasts; often times occurring whilst wearing a sports bra.

3. Boobs that appear small while wearing clothes; but are actually not in the nude.
Damn, that shortay has some kick-ass ninja boobs.

Girl your ninja boobs, snuck up on me like Jake Gyllenhaal on Heath Ledger.
by Ninjaboobgirl4U January 25, 2010
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