It's expected that people tip a waiter for their service.
Rin, who is at a restaurant,has waited a long time for her steak meal to come out and when it does it's overcooked.
Rin wants to show how unhappy she is with the meal.
Rin points out the problem with the steak and leaves an average tip for the service.
Rin tells the server about the temperature of the meat and leaves no tip.
The server is relieved to get a tip even though there was a problem with the food.
The server makes less money for the day because of the chef's mistake.