dirty rat

slang

1. A despicable, deceitful, treacherous person. The governor is blaming corporations for the damage to the environment, but that dirty rat helped strip away environmental protections when she was in Congress. Your agent seems like a dirty rat, so I wouldn't sign any contract he gives you. Mom, anyone who asks for your Social Security number on the phone is just a dirty rat trying to steal your identity.

2. A criminal who betrays or informs on their associates. The boss sent some thugs around to Tommy Fisk's apartment to put that dirty rat in the ground. Ray will find the dirty rat and take care of him—behavior like that does not go ignored. I bugged that guy because I suspected he was a dirty rat, and, what do you know? He went straight to our enemies.