A member of a not-so-secret and vaguely homoerotic society originating in Danville, California. A Nipple Ninja is fluent in many techniques of nipple flipping, and performs his art on unsuspecting victims. These moves (examples include: The horseshoe, the rainbow, the monkey wrench, and the Horny Hungarian) can be performed in friendly or unfriendly situations.
Holy shit, that Nipple Ninja just pulled a "guillotine" on Madlwski's fat nips.
by Steve Kaye December 03, 2005
A person who can grope a females breasts without being caught or causing conflict
That guy is a fucking Nipple ninja
by Nothunterself December 16, 2013
What a baby is called when displaying innate ability to fend off removal from the breast when feeding.
"Agghhh, the Nipple Ninja is chewing my nip, but I can't get her off!!!"
by Annie's Mum May 11, 2009