It's in any customer related business.
"I'm the paying customer and I get what I want!" is the typical attitude.
My typical response is one of two...
"If you want to speak to me like an adult without yelling we can correct the issue."
"If you continue to yell and be belligerent I'll just walk away and then I'm not helping you at all."
You still get some that carry on, it's entitled nature.
Almost thought I had to put a customer in a choke hold once they way he was going at the service manager.