I had the kinds of problems with people you mention when I was in retail.

Since I was seeing a psychiatrist at the time for depression and anxiety, I asked for some advice on this issue. He suggested I make a little game out of my time at work.

He said: "Imagine that you are working in an insane asylum. The people who are rude to you are all mentally imbalanced in some way. So you are just humoring them when they are acting out, knowing in the back of your mind that they are crazy."

I tried this and it helped a lot although I still had times when stuff at work got to me.

Wish I had something more helpful to offer. I think that people in general are becoming less civil in society. That is probably a gross overgeneralization, but it has been my personal experience.