Reverse Prolapse 

When you butt clench so hard that your anal cavity crawls even further into your body instead of exposing itself outwards.

Jake: Wow I just went all in with Kings vs Ace 10 in my poker tournament.
Dave: Did you win?
Jake: Yea but I was so nervous :(.
Dave: Was it bad enough to reverse prolapse?
Jake: That is what happened lol xD :'(.

Reverse Prolapse by g-of-the-g-unit March 29, 2013