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1.
A hot, smelly gas bubble expelled from the anus thus causing a burning like feel around the anus, sounds wet but sometimes silent and simultaneously causing a disgusting, panic causing, rotten-egg like aroma. Basically when you have the craps and your stomach is bothering you,most of the time those wet sounding smelly farts you squeeze out at that time is an acid fart my friend. Enjoy them.
Dude,I let out the worst acid fart in Debbie's face.

I thought I was going to shart but I just released an acid fart.
by tophieCC January 15, 2009
 
2.
When someone needs to make diarrhea and accidentally farts, spewing some out into their undies, thus burning a hole in them.
Damn dude, I never want to have another acid fart again
by Pete "Meat" November 19, 2007