Here's my favorite tipping story.
I used to travel quite a lot for my business - pretty much with the same people each trip, for four cities a week. With that kind of intense interaction, it's a killer to be with someone you don't like.
One guy I traveled with would carry around a pocket full of one-dallar bills (multiple reasons for that, but I digress). At each meal, he would put a small stack of them on the table. When the server came to the table for the first time, he would say, "See that pile? It will stay that big if you do the following..." And then, he would list the things he felt were required for good service. As the meal went on, he would make a big show of taking bills off the pile.
His standard was that GREAT service deserved 15%; good service was 10%; and bad service was zero. He used to ask each of us what we tipped. At first, we would tell him - assuming he was just having a hard time with the math. Then, a few months into it, I noticed a pattern with him. We would all head out to the rental car, and he would always need to go in to grab his forgotten jacket, use the restroom, etc.
So, you see where this is going? I followed him one time, without him knowing it, and caught him TAKING CASH OFF OUR TABLE. What a colossal douche! We made his life miserable, after we found out. His justification was that he thought tipping so much was immoral, so he was helping us out by taking cash off the table, from whomever didn't pay with credit card. So, if the cumulative tip was, say, $40, he might take a cash-payer's tip down to zero, to bring the whole table to 10%.