2 friends and I went out to eat yesterday after school/before our carnival. One friend and I paid by credit card. The other friend paid in cash, and told him she didn't need change. Her daughter is a waitress so she always tips nicely and we had had excellent service.
The waiter came back with the credit slips and her money. He asked if he had dropped money when he walked away. Turned out that friend had misread the total and given him to little money. She apologized and gave him the correct amount.
We all agreed he handled it very diplomatically - especially since she had made it clear she thought she had included a tip in the original amount.