At first when I heard stories like that, my initial thought was "Good. That's what the people get for having bad attitudes." But then I thought about it, and I realized that is a horrible attitude for employees to have.
I worked at a daycare for two years, and my job was to watch after little children (obviously) ranging from the ages of 1-year-old to 5-years-old. Parents were generally nice people, but there was always that one parent every now and again that would have a bad attitude. Now, according to restaurant and hotel employees, my response should have been to give the patron poor service in return. One has to wonder, how would you give poor service at a daycare? Well, I imagine abuse would be the most obvious way. "You wanna talk bad to me? Well, I'll just slap your baby when you leave." ... Obviously, I never abused the children I watched. That is absolutely abhorrent, and I loved the children too much to ever even think about abusing them. But poor attitude equals poor service, right?
How about when you go in to get your car fixed. Maybe you had a bad day, and so you snap at the man at the counter. When you get your car back, you find out your tires have been slashed. You can't prove the mechanics did it, but you deserved it. Poor attitude= poor service.
Maybe you need to go to the dentist (oh yes, I'm going there. Cringe). You are again having a bad day, and so you snap at the dentist when he comes in to drill that cavity out of your tooth. He "accidentally" drills into your gums. Oh well. Poor attitude=poor service. Deal with it.
Obviously, I am being entirely facetious with these examples just to prove a point. My point is that no person should think they are entitled to give poor service just because the customer has a bad attitude. If a person chooses to take a job where they are working with customers, they need to realize they will encounter people of all walks of life. Nice people, oblivious people, rude people, psychotic people (well, one would hope they don't meet psychotic people, but you never know). Whatever the countenance of the person, as a mature, responsible employee, people are expected to give decent service to everyone (barring any extreme cases, such as psychotics that get out of hand, or angry drunks, or something of the sort).