Defining Discourtesy

I posted on Facebook recently, "Courtesy trumps all." The post garnered a number of comments from people who agreed with me. Without exception then mentioned that "please" and "thank you" always were best for people to remember.

That's certainly true, but I find that many discourteous people hide behind a smoke screen of please and thank you and get credit for being polite people.

The discourtesy I dislike has to do with what people actually do--or don't do.

I think I wrote about this recently, and I'm repeating myself. I'll have to learn to deal with it. Is dealing with it simply ignoring discourtesy, telling a person they're being discourteous, or shunning the person in the future?