It all boils down to being courteous to each other. When I worked as a cashier, I encountered people who were unbelievably rude. Apparently, she didn't realize that I, too, was a person. Customers should understand that cashiers are not well-oiled machines. They are human beings and should be respected as such.
Many servers have a lot more class than the people they serve.
I've always enjoyed them. It was there that I ran into a handsome young usher who was working his way through college. I told him I was looking for my little brother. He knew I was lying, lectured me and then asked for my phone number, which I promptly gave him. We've been married 49 wonderful years, and I never lied to him again.