Villains should use insults when talking to the PCs, of course. But it's difficult coming up with truly inspired insults on the spur of the moment when improvising the villain's dialogue. So prepare some original and artistically crafted insults beforehand and have them on a list, ready to pepper into the villain's conversation at appropriate moments. (Like every second sentence.)
The list also comes in handy when telling your players to stop mucking about, quoting Monty Python, or discussing the latest video games, and play the actual game.
Obi-Wan: Oh my god. You were once Valorum, the Chancellor.
General Grievous: Irrelevant! That name no longer has any meaning for me.
Obi-Wan: The Republic has you listed as a missing person.
General Grievous: Person? Ha!!
Anakin: So... What are you up to?
General Grievous: My armpits in incompetence!
General Grievous: My glorious cyborgs have been relegated to guard duty. This nanny-coddled lickspittle of a pilot barely even crashed into Dookû's ship at all!
Dofine: Rook after Grievous, he said... Lepair your leputation, he said...
R2-D2: There's a secret to managing out-of-control fellow party members.
Dofine: Rearry? What is it?
R2-D2: Sorry, it's a secret.