"Surely we all have at least a vague idea of what boys get up to?"

I would say the answer to that is no. Unless we look at studies done by qualified people because we don't. I can say this because unless you have asked everyone you know about this topic, which I have not, then you would really only know about your own experience as I only know about mine and the few people I know who have told me about theirs.

I'm just trying to point out that what you are saying is 'assumed knowledge' that everyone has is not so because everyone's experiences are different.

Gs