1. when one eats a delicious dish of mexican cuisine, but afterwards suffers the consequences in the form of uncontrollable, firey diarrhea.
2. when after recieving anal sex from a person of mexican heritage (or hispanic in general) one contracts an STD in their anus, resulting in a sloppy, muddy butthole.
Person 1: Dude those burrittos were awesome, but i'm never eating there again.
Person 2: Why's that?
Person 1: Because i was on the toilet for the next 2 hours with a case of Mexican Mudbutt
Lisa: Jenny, how'd things go with Jose last night?
Jenny: Well i let him do me in the ass, and now i think i've got a sloppy encounter with Mexican Mudbutt