Snaggletoothed, whorish looking smile. Typically a trashmouth girl will purse her lips in a tight, strange manner to hide her fucked up teeth. See country singer Jewel. Note that not every trashmouth girl is a cock gobbler - but most of them are.
Bob: Look at that fucked up grill. What a trashmouth!
Shawn: She's had more dicks in her mouth than dental visits, that's for sure.