Huh, so I just got a call from the shop owner. I guess he had a talk with his a-hole peon and heard about our exchange. He said he'd intended to not charge although that wouldn't have been "to rule". I guess he hadn't filled in "Mr. Blackmail".
We didn't get into the details of my conversation with the a-hole, but the upshot is that the owner of the shop will credit me my $20 bucks the next time I come in.
Good thing I haven't yet won that raffle and thrown the prize bike through his storefront window. That would have been embarrassing.