The feeling of utter discomfort one gets from a combination of eating spicy or hot food, making a torturous bowel movement, inadequatly cleansing their butt hole and or crack, and being so hot, that one sweats in the crack of their ass, causing a witches brew of catastrophic proportions in the rectal area. Taco ass can be further irritated by chafing from activity(i.e. walking,running, etc.), or chafing from being extremely fat.
Damn it, I guess I didnt wipe good enough, I have some bad taco ass!