Ever tried to think from the point of view of a waiter or a waitress? I know it is not that relevant for people who do not work as them, but there is much more than what actually meets the eye. Every day almost every hour in their profession, they come across different people who they are unaware of. And they have to patiently deal with them, however well mannered they might be or snobbish they could be.
For those people, the more diplomatic way out is the best option but why give them a chance to have to take that route. Whatever happens in their personal lives is a different matter altogether but after all or rather before everything, they too are human beings just like you and me. Eve they have a right to be treated fairly and well.