My older son was a macho posturing youth at one stage. We were out together when he was about 15 or so, a rare occurrence at that age. Out of the blue he did this very thing, I was startled and really angry with him at the time and I have to admit it brought out my inner Margaret Thatcher and I hand bagged him there and then. It was a knee jerk reaction, please don't report me to Childline retrospectively anyone, I haven't done it since and I'm happy to say that he no longer spits in the street!