The customer is always right
If you ask us, these customers are definitely right, and they did the right thing leaving the waiters this message. There’s almost nothing more frustrating than waiting for service at a restaurant, and it gets worse and worse the hungrier you get. People can get pretty reckless and impatient when they’re hungry, and waiting for service for over 30 minutes is not reasonable.
This group of people waited patiently for 30 minutes, without having a single waiter acknowledge them or approach them, until they have finally decided to leave, not without giving them a piece of their mind, in the form of ketchup and mustard. As they were cleaning this table, the waiters had a chance to think of their work etiquette.