When having a bowl movement, the stool is nearly liquid, and burns not only the intestines, but the sphincter as well, leading one to believe their rectum is on fire. A more common term that would be used as a noun would be "Lava butt"
Dude, last night after downing a bottle of tequila, for no reason at all I consumed a ton of chili peppers! I was awoken the next morning to FIREAH, I haven't left my toilet in hours.
by WaldoBro123 January 04, 2010