I quizzed him a lot on this point and i suspect the truth...

I quizzed him a lot on this point and i suspect the truth was that it was like a lot of things at that age: you don't have any clear reason, you just do it. You do it because you think it might get a laugh, or because you want to see if it'll cause a stir. And when you're asked to explain afterwards, it doesn't seem to make any sense.