Annoying children have oblivious parents

Have you ever noticed in a large or small gathering of people that there is always one child that is annoying? Why is it that the parents of that child are oblivious to his/her actions? This evening I took Johnathan to his last cub scout den meeting and as usual there was one child totally out of control and interrupting the entire things. This child's parent just sat there the entire time ignoring the behavior while us other parents kept looking at one another in amazement. I would have been mortified if my child was acting up and being disruptive to the group. I would have had no problem grabbing my child and leaving if that is what it took. I wonder if the parent noticed the behavior and was embarrassed and didn't know what to do, or were they just used to this action and just accept it as the norm. I know that my child would not have gotten away with this action. I would have had no problem grabbing my child and leaving if that is what it called for. I wonder if that child acts like that in all situations?