Mexican butt-worms are what you pick up in mexico after eating from a taco cart or tamale stand that is less than sanitary. They are also different from other butt-worms because they wear sombreros.
Did you hear about Steve's trip to Tijuana? He got a bad case of the mexican butt-worms after eating at a filthy taco stand.
Maddie: "I was wondering a dark alley, when all the sudden this mexican jumps out of nowhere, shoves me head first in a garbage bin and mexican butt raped me. Damn that burrito was extra hott"