As we left, I was last f-i-l in front of me. We passed the waiter, who held the tip tray out (the bills were spread, like a poker hand) and he said:
"Sir? I believe you may have made an error..." (as he said this he tapped the bills)
f-i-l w/o missing a beat said:
"Oh, I think you are right. Thank you for telling me."
He then reached out and took a 20 from the tray (the service had been terrible).
Hahahahahaha! I would have paid money to see that!