Claim a man makes when he wants to boast about his penis size. The inference being that the third leg is his penis.
Julie stated to Mark, "Why would I want anything to do with your two inches of hardchode dick?"
Mark replied, "Shiiiiiittt girl! I am a three legged man! They call me tripod."
When a guy's fat gut is so huge it resembles a hippopotamus head ... it therefore must be a hippopotamus that only has 2 legs and has purchased itself a lovely man's head for a hat (probably not such a lovely hat given the size of the gut)