I have a couple of stories, the first one on myself.
I was in San Diego with a friend for a three-day pleasure trip. We were doing some sightseeing, shopping and eating out. One night we went to a well-known bayside fish restaurant for dinner. It was lovely and delicious. She gave me cash and I paid the bill and tipped well. At least I thought I did.
We were on the stairs going down to the parking lot when the door suddenly opened behind us and the waitress rushed out. She cried out something like "You didn't pay your bill." I remember standing there stunned for a few moments while that penetrated my brain. Then I sputtered "I didn't???" while reaching for my wallet.
Turns out I didn't. What I must have done was take my friend's cash and put it into my purse without realizing it. I was humiliated that the waitress thought we were attempting to steal from her. I was so embarrassed I couldn't look my friend in the face as we headed back to the hotel. It was just one of those brain drain moments that unfortunately makes one look really, really bad.
The second story took place several years earlier. I used to live in Hawaii and was a runner, a member of the marathon community. Every Sunday morning after our long runs a group of us would head to a local restaurant for breakfast. The group varied from about five or six to a dozen or so. And because the two primary people, the hub as it were, were two slightly older men who were well known to the manager and staff the group was seated in a closed-off area and given special attention.
One Sunday the waitress working our table was not particularly good. I can't remember if she had us before but the service was fairly poor. I can't remember who started the conversation, but I talked to one of the two primary guys who that morning had picked up that tab about tipping the waitress. I guess I wanted to know if he had left a quarter or nickel. He told me something I have never, ever forgotten and have utilized myself ever since then. He said when the service is bad or only fair he still tips the same as if it had been superb. But he also calls the waitress over and as he hands it to her he tells her that her service was not good and why.
When I asked him why he did this he said that anyone can have a bad day. He believed that by doing it his way he ensured that her day would be better, that it was a classy way to handle it, and that he would be remembered the next time he went back. He felt strongly about doing it this way, and I was so impressed with his way of handling it that it became my practice as well. (Fortunately, it has been a very rare occasion when I have needed to use it.)