Dumb new idea for that scene:
Trooper: “Who’s your operator?” or “Who assigned you here?” or something like that.
C3P0: “Oh, Babu Frik! He’s one of my oldest friends.”
Trooper: “Who’s Babu F-” gets shot
I really like this. Could even keep the same “Then why are you… wha?-” part?
Obvious explanation, but; the Trooper continues with the next part of his same old, same old soldier speech until he realizes he doesn’t know what a Babu Frik is and he’s caught off guard. Then blam. Extra funnies without being too on the nose! We know the Stormtrooper doesn’t know who Babu Frik is, and so he does not have to literally say his name for the beat to be conveyed as funny.