1. the sensation that comes when one eats some spicy food (maybe some korean barbecue or a volcano box from taco bell) and takes a dump later on during the day, and feels as if his or her butt knew that the food was spicy.

2. a feeling burning around the anus after eating spicy foods and eliminating the resulting stool

note: the foods causing fire butt are not limited to spicy food.
"Hey, how's it going"

"Man, I had some volcano nachos this afternoon and I just took a deuce. Feels like my ass is on fire."

"You, my friend, have fire butt."
by kevlarcasm December 15, 2009
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The incredibly painful stinging sensation one receives on their anus, usually caused by indigestion and/or spicy foods.
I love hot wings, but they give me firebutt.

Sorry honey, we can't do anal tonight, I've got firebutt.
by CritzCrakka August 26, 2006
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