Another great observation! I've noticed the same thing. I guess it's something people in the service industry would tend to notice. I've also thought this...being angry all of the time is exhausting. I'm serious. It drains your energy and makes you more irritable. Then, it just becomes a vicious cycle.
It's true..... we notice interactions between people all day long. It's easy to tell nice people from mean people when you get to see people talk to each other all day.
Being nice and being happy will also keep you healthy. Thanks for the resteem.