when a man tucks his erect penis between his legs and presents it to another person to suck from behind.
i was feeling frisky so i gave the woman the old undertuck n' suck
by blumpkinboychaps April 4, 2009
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The dark side i mean the under side of your scrotum. Usually has hair and is right next to the taint .
Ben stop looking at my undertuck just continue licking
by _____ June 22, 2003
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