I think that disresepect has always been with us. When I was a child, the majority of classmates were friendly and courteous, but there were a few who were discourteous, although rarely to the extent that we see now.
Television and film have raised the bar for what is acceptable. Rudeness is celebrated and crude language that we do not use in our home is not uncommon.
So I think two major factors are at work:
1. Print and electronic media scour the globe for bad behavior, so we are exposed not only to our personal pool of people who do not adhere to our standards of behavior, but also to everyone's pool around the world. That is to say that we are aware of a much wider pool of malefactors and discourteous persons.
2. The standards have changed. By prevalent standards 60 years ago, today's children are wildly out of control. By current standards, they are merely freer to express themselves. Children are no longer seen but not heard. They speak out and believe that if it is true, rudeness is not a factor. It is merely freedom of speech, as they understand it.
3. The children who are rude are so confrontational about it that it feels more widespead than it is.
Despite the foregoing, the vast majority of the children I see are well-mannered, even by my standards from 60 years ago.