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Knubbin (pron NUB - IN)

The bump formed in your fly while sitting down caused by your zipper. Sitting down causes looseness in the material surrounding the fly and the less flexible zipper, velcro, button, etc, forms into a funny shaped lump.
Ted: Hey look, Fred's got a boner! Haha!
Fred: Na way man, it's a knubbin
by Aceramic May 29, 2009