Found it! It's from 'The Sound of Music - Hazzard Style' (also in season 4). The federal officer confronts the boys and tries to identify himself, but he has a problem there:
Ben Jordan: I seem to have misplaced my wallet.
Bo: Mister, we've heard that 100 times.
Ben Jordan: You just take my word for it. I am a federal officer.
Luke: Sure, and I'm Santa Claus, this here's Bugs Bunny.
The episodes had different writers, so maybe the two Bugs Bunny references were a coincidence.