He was called 'Dirt' in the storyboards until "Professor Chaos".
Dog Poo made his first prominent appearance outside of aforementioned episode in "It's a Jersey Thing" as part of Cartman's entourage against Kyle. He is the only member besides Butters to have lines, yelling "GET IT OFF OF ME!" when Snooki rapes him.
He has messy, faded brown hair, and wears a messy brown jacket with dark green trousers or track pants. He has a mark on the left side of his jaw that may be a large mole, scab, dirt stain (similar to Pig-Pen from Peanuts), or actual dog poo. And on the right side of his jaw a scratch.