When one urinates through the legs of another person who is defecating.
Pisser: "Bro, I really gotta piss!"
Pooper: "Dude... I'm taking a shit"
Pisser: "Whatever bro, lets muddy waterfall!"
1. another word for diarrhea
2. used to describe a condition in which after anal sex, a mixture of semen and feces drip out of the anus.
1. Because I ate at taco bell, I had a muddy waterfall last night.
2. The bed sheets got wet from the muddy waterfall.