Any form of explosion just inside the anus. Could be the result of inserting and igniting gasoline or gunpowder, attempting to light a fart, or that Mexican food from yesterday. Depending on the strength of the sphincter, severe anal combustion may result in blowing out the anal socket or rupturing of the rectum.

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When a women shuves a buttery dildo into her anus, she contracts her but muscles so the the butter oozes out. This is tipicly stereotyped to fat or obese women. An extention of this is when the used butter is used on toast