An extremely despicable, untrustworthy, immoral person. I took Charlie in because his sister begged me to help him out, but that rat bastard robbed me while I was sleeping! There's no way I'm trusting a rat bastard like that to run my company.
n. a really wretched or despised person. (Rude and derogatory.) Stay away from Albert, he’s a real rat-bastard when he’s drunk.