A horrible and disgusting form of diarrea that fills the whole toilet with its volume and the whole house with its odor; is usually due to consumption of fast food or drinking lots of alcohol the night before.

"Dude, why are you clutching your stomach with one hand and covering your ass with the other?"

"Fuck, I knew I shouldn't have mixed rum with pabst with gin with taco bell with a big mac last night, now I have to take the biggest McNasty known to man."

The Urban Dictionary T-Shirt

A female that has taken disgust and grime to an extremity, a true whore at heart that reminds every man of something that can be purchased at mcdonalds; fat, sloppy, and down right disgusting. Generally, if you are indeed dealing with a true McNasty on your hands, chances are that she is so loose that a football can get inserted with zero difficulty.

Guy 1: Wow bro, every time I turn around that girl is hooking up with a new guy. I can't believe you got with her!