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1.
When males partake in polygamous anal sex facing in the same direction, i.e. nut to butt, so that the orgy resembles a centipede. Although only a true centipenis can be made with exactly 50 participants, any group of 3 or more is commonly refers to as this for comedic purposes.
"Did you see the MMMM scene in that new pornographic video, 'The Human Centipenis'?"

"Yes sir, I thought Scotty Aces' middle performance was worthy of an AVM."
by Scoops747 July 03, 2013