event - While attempting to stick a finger, animal, or other foreign object into a partner's anus, a Bucharest Backfire occurs when the partner farts (or, in the worst case, actually defecates), rejecting the foreign intruder. Extra points if, while ejecting the finger, the fart sounds extra loud and high-pitched.

origins - The saying is thought to be based on the fact that Bucharest, the capital of Romania, is a shithole. Like a banshee ejecting an unsuspecting tourist from Romania, sometimes a person's ass has its own similar defense mechanism.