I used to serve the lunch shift at a restaurant right across the street from a hospital. We offered the hospital employees 20% off so needless to say many of them would come in to eat. The problem is that a lot of times the people who take advantage of these types of discounts are not the ideal customers to serve, and this was no exception.
One day over the summer I had a table of two women from the hospital who all the servers in the restaurant knew about. They came in all the time and were rude, needy, and never left more than a 5% tip. That particular day we were very busy. I had 4 or 5 other tables, and they had me running all around the restaurant trying to fulfill their stupid requests. At the end of their meal I presented their bill, and the first thing they said was a sarcastic comment asking if I had remembered to put "their discount" on the bill. Of course I smiled and politely stated that I had remembered, while at the same time wondering how she didn't see the discount circled with a bright yellow highlighter like it is every time. As soon as they left I went and picked up the check. They had left me a $2.13 tip on a $42.87 bill. However, they had also left something else. A large key ring of hospital keys was wedged in the booth where one of the ladies was sitting. It had been brought to my attention by another hospital employee who had lost her keys earlier in the summer that they aren't standard keys. They are a special type of key that is very expensive to replace, and that cost has to be covered by the employee that loses them. About a half hour later one of the ladies came back and was frantically looking around. She saw me and immediately ran over to ask me if I'd found any keys that she might have left there earlier. Of course I told her no, and took her information in case anything turned up. On my way home that night, I made sure the only one who would ever see her keys again is the fish that live in Lake Michigan. I'm sure she'll have no problem replacing the keys with all the money she "saved" by not tipping us.