It is in a waitress’s very job description to be nice to her customers no matter who that customer may be. Also in the job description is to take orders, serve food and beverages, and bus tables. During all of those tasks she is probably smiling and being as pleasant
Everyone should work in a restaurant at least once. Ask any server, bartender, barista, cook, dishwasher, buser, greeter, and they’ll agree. It’s a conversation I often have with other people in the restaurant industry. This conversation is half bitching about customers (sorry not sorry) and half enumerating all the ways that working in a restaurant makes you a better person.