When a man fucks a woman/man in the asshole and an air pocket forms from the massive pressure of him going in and out of his/her asshole. The air pocket begins to grow like a balloon and the pressure becomes very intense. Then, when the man cums in his/her anus, he pulls out and the pressure from the air pocket shoots out a mixture of shit and jizz all over the man's private parts. Usually, the man doesn't expect it.
bob- (finishes in jenny's butt) "that was awesome babe!
jenny- okay pull out my asshole hurts.
(LOUD POP NOISE AND THE POOP AND JIZZ SPLATTERS ON BOBS JUNK)
Bob- WHAT THE FUCK!
Jenny- I'm so sorry babe! i didn't mean to rofleblober all over your junk!! it won't happen again!