Oh, I've left a penny tip for a waitress once... I remember ordering a specific beer and she said they were out. A table next to ours ordered one about 10 mins after I placed my order and they got theirs... I was like WTF?

On top of that, took forever to get our food and it was cold... I was not a happy person that night.

I also subscribe to the art of trying to leave a cash tip so they don't have to pay tax on it.