In almost ALL cases it's the parents fault. Period. I can't tell you how many times I've wanted to smack some rowdy, out of control, or disrespectful kid. I have to calm down and remind myself that it's the parents who are responsible for teaching, monitoring and diciplining their kids. If the kids aren't taught right/wrong and respect by their parents, they'll never know the difference.
I have three kids and I'm tough on them. I demand that they show respect to others and behave themselves wherever we go. I've been accused of being too hard on my kids, but I've had twice as many people compliment my wife, myself and our kids on how well behaved and nice they are.
Now, most of the time I want to smack the parents. I've got in-laws that should be beaten for their kid's behavior.