If the server was saying they were shorted 15 cents of their $80.00 tip I agree that is pretty tacky. I would have asked them to explain the shortage in the event that I made an error. If they were truly short the 15 cents after the explanation I would told them that I was sorry and that had I known they were going to be petty over 15 cents on an $ 80.00 tip In would have left a smaller tip to match their gratitude.