sounds to me like he's testing the waters?!?!?! Cheeky little monkey. I think you just have to keep telling him that it isn't acceptable behavior and then ignore the fact that he does it. Cohen went through a similar stage at 6mths and I would tell him, "Cohen you mustn't do that, that's naughty!!" He would just blow raspberries at me and keep doing it. I would say it again and then just ignore him after I said it the second time. I think he realised that he wasn't getting my attention and that I didn't think it was very funny (I laughed the first couple of times.....naught, I know but it WAS funny at first) and soon after he stopped.
Don't know if this helps you much but just thought I would share my experience. Hope he stops for you soon!!!