I don't understand mean people!

I can kinda understand mean kids, maybe even mean old people, and really poor people who are mean, - but certainly not mean middle aged people. People who are supposed to know better, people who go to church, people who are better off than so many other people.

Why are they mean? What's that about?

Is it a wiring problem? Has something come loose in the little wires up in their grey matter, wires that influence their ability to keep their mouth shut if they can not say something nice, wires that help them realize the world does not rotate around them, wires that help them get over whatever crap has happened in their life and not to blame the rest of us for their unhappiness?

What does a person get out of being mean? Does it help them sleep better at night?

anyone with ideas? Please advise me asap!