... without trying to pass any sort of judgment here, you do realize you have the right to reject/refund someone's order without having to explain yourself, yes? Or at least make it very clear they only get X number of revisions to a piece, if any?

I've gotten a few weird clients too, but damn, man, if you knew this guy was bad news in the first place based on his at-con behavior, you shouldn't have taken the order.