Although David's points have a lot of value to them, we are living in an age of extreme uncouthness, selfishness and narcissism.
That won't change until those adversely affected demand better behavior. And I would add, that all of us are guilty of these same sins at times.
Recently, I had an example of this thoughtlessness pulled on me. I was walking, in the general direction that most of those around me were proceeding some in opposite directions. For clarity let's say the general flow was proceeding north and south.
Along comes a young man (they are almost all younger than me these days) moving crosswise or perpendicular to the general flow. He proceeded to step right in front of me almost causing a collision. As he passed merrily on his way he said in that superior put down way, "Excuse you!!!!" implying I was at fault and of course, should have automatically stopped as he was so superior. I just shook my head and kept walking.
There are some obvious exceptions to the above. Parents and others in authority roles need to do a much better job of teaching respect and correcting the errors of those in their charge. In cases where the behavior of the offender and/or others may be at risk immediate action may be called for.