I used to waitress & there were certain types of people who never tipped....
I remember these 2 professional women who always came in & never tipped......the hostess always sat them in my section & they asked for a knife, I brought it back then they wanted something else & on & on.....basically I couldn't pay attention to my other tables cuz of these 2 & then they didn't tip.....finally one day I brought them their food & their check & told them since they didn't tip I wouldn't be bringing them anything else & if they ever sat in my section again I wouldn't wait on them at all........They said "What you expect us to tip you?????" Like they couldn't believe that they should tip me........I slaved over them & was nice..........well not any more. So there. LOL