I've had nothing but customer service jobs and after twenty years my conclusion is the vast majority of people are pretty okay.
A few of us, however, are just stupid, petty, hateful sacks of runny goat shit. If I had to guess -- and I do, I'd never dream of encouraging these people to tell me MORE than I already have to put up with -- I'd say they are powerless and unhappy in their own lives. Because they are stupid and hateful, they would never create anything positive to improve their situation. The only way they know to feel better is by shitting on someone else. Because they are cowards, they do it to people who aren't free to tell them where to stick it. It's a cheap, quick, safe way to make someone -- anyone -- pay for their unhappiness.
If it's any consolation, that dipshit will quite probably never experience a good day. He'll always feel unhappy, powerless, shortchanged, and victimized. The closest to genuine happiness he'll ever get is the bitter satisfaction of telling you to fuck off. If you've had one moment of real unfettered joy in your life, you beat him.