Used to eat in a small town diner often, same waitress was always there. Poor gal worked her but off and a bunch of cheap locals hung around and drank coffee leaving her change on the counter.
Always ordered the same breakfast and basically tipped her 100%, was cheap and she was pleasant.
Had been years since I had been in there, walked in with the wife and she came over with her typical smile and asked if I wanted the usual, was the last time I was in that place and I left her 20$ for a tip for a 20$ breakfast.
Tip according to the service and food received.
I work as a guide, very seasonal, crazy hours during season and a lot of time away from home, friends and family. Tips are much appreciated, however I wouldn't expect one if I was a sh-t guide!