This is a sex act in which the receiving partner is bent over and taking it in the ass. Then, right before climax, pull out, flip them over on their back, and quickly jizz in their eyes. Then, kick them in the side of the leg. Now, their on their three remaining limbs with their eyes closed shut, and viola! A Three Legged Chinaman.
Andy: "So dude, I gave the 'ho a three legged chinaman last night!"