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1.
unsatisfying coitus with an extremely small penis... so small, in fact, it is sucked up into the man's body like the head of a turtle, nearly making intercourse completely impossible altogether.
Brian: "It's just sad when you please a women and they go crazy. She was begging for another donkey punch."

Kelly: "...more like a turtle thump"
by havwingswillfy April 08, 2010