An incredable painful feeling in the anus as if acid has been poured in with a funnel, usually after over indulging in spicy foods in the previous 8 hours.
Person A : Ahh man, I have awful acid arse this morning
Person B : What did you eat last night?
Person A : A large vindaloo, spicy onions and pakora with hot sauce followed by a large spicy meatball pizza with Jalapenos.
Person B : No wonder, fuckwit.