A does something slightly similar...
He likes to shout things like "Big fat boobies" and will pull at my tops to look etc. He has a sister 2 years older than him and a sister 18 months younger and the girls call their privates a "kipper" He has said in the past when they have got dressed that he wants to see more kipper and physically tried to remove their underwear
He also plays with his "dinky" a lot and likes to show it as often as he can and will pretend to pee on people and has actually deliberately done it on one occasion that I know of, so I sent him up stairs to finish peeing in the loo
He likes to be naked and will show his bits a lot. He will rub himself on his sisters too, but they can't seem to get him off them because he's so strong :o so we have to intervene. I don't know why he does it and he says he doesn't know and laughs when asked why he does it. He likes rubbing himself on my leg too (almost like a dog would) when he is stopped, he will punch himself or me and throw things and come out with a LOT of bad language
I have never mentioned this to anyone before, but I am thinking now maybe I should have