J.D.
All I can say is that it is probably just a stage. He will get through it and the best thing you can do is ignore it. If it bugs you, just leave the room he is in. It really is something he is doing for himself and should not be punished for it. In fact, the more things you do give him attention for this behavior and lend to it continuing.
As with most things, you just have to remind yourself that you don't see adults with this behavior. This too shall pass.
GL!