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1.
It is from when you eat spicy foods and later on you feel the burn on the butt.. It feels like acid.. hense the term acid ass.
Dude i ate some mexican food yesterday and i have some serous acid ass today
by THEBIGO August 07, 2006
 
2.
someone who has farted and it burns your nose hairs
damn roberto is suffering from a case of acid ass
by FRANK September 30, 2004