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when you're making out with a chick, and you slide your hands down her pants and pinch her bare ass. UNDERBITE!!! see the intruder...
i gave my roommate's mom the underbite last night.
by nate fingerman July 16, 2006
when your eating pussy and you get a mouthful of shit
Fuckin Bitch, I just got an underbite.
by AlBundyisgod1906 April 09, 2006