When a man is wearing tight pants and the crotch seperates his testicles showing a bulge on each side of the seam.
Look at that guy, his pants are so tight I can see his sack Knuckle.
by Otis The Duke January 26, 2009
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A tight sack with defined hemispheres male camel toe.
Roger came out of Bellagio's pool sporting a small Knuckle Sack
by Ms. Vegas May 26, 2016
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