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1.
Sour ass is an uncomfortable condition caused by ass cheese, which is typically the result of inadequate ass wiping. As ass cheese is left unattended for some period of time, it mixes with sweat and heat, and begins to cause irritation and itching, between the buttocks and around the anus. This irritation is referred to as 'sour ass' and is exacerbated by warm climate conditions. It is a highly uncomfortable condition which is resolved temporarily by wiping the ass with wet tissue or baby wipes. However, in order to fully resolve the condition, a shower must be taken, along with a change of under-bottoms.
Chip thought he had wiped his ass enough, and returned back to work doing carpentry. As the hot 98 degree day progressed, he realized that he did not wipe adequately, and ass cheese began to accumulate around his anus and between his buttocks, causing a severe case of Sour Ass. He tried to resolve the condition by digging his hand into his ass, essentially wiping with his underwear. However, the foul smell was detectable even in the outdoors, and he had to return home to take a full shower and change his underwear, which now contained long brown skid-marks.
by Tom Haranger October 31, 2007
 
2.
A gaseous interruption that is so foul and sour it has the ability to knock those around it out of slumber. Often confused with the stench of a dead animal.
Put a cork in your sour ass. What the hell did you eat yesterday?
by SKBO June 24, 2005