Mudders

Mudders are a slur-term for Mud-Men or "Mud People" that is a mix between "Nigger" and "Mud-Man", and it's usually a common phrase in L4D2 matches when someone spots an uncommon infected, that is, a Mud-Man.

Michael: "MUDDERS?! AGAIN!?"
Lucas: "FUCK MUDDERS!"
Mason: "MUDDERS ARE GAY!"