Of course there's a trope for this.

Take any opportunity you can to play this one into a game. As soon as any PC starts talking badly about someone who is not present - see if you can make them present. It's not always plausible, but when it is it's worth the effort!

Transcript

Commander Igar: I mean some people get hit with the ugly stick, but this guy grabbed it with both hands.
Commander Igar: Stupid too. Just stood there while we nabbed him. Not too much brains in this family.
Commander Igar: I bet his mother was in-bred with a space avocado.
Commander Igar: Probably had an affair with a Bantha, resulting in this misbegotten yokel.
Luke: Be careful insulting my mother.
Commander Igar: And why? I'd say it straight to her face! If I could stand looking at it!
Commander Igar: I bet her face could launch a thousand ships - fleeing in terror!
Darth Vader: Let's go, Luke.
Luke: Okay, mum.
{beat, Igar stares}
Darth Vader: You know what to do.
Commander Igar: Yes, sir.
Commander Igar: Um. Ma'am.