Where are your shorts?

Got Isaiah home from daycare and in less than five minutes he had stripped down to his shirt and underwear. He leaves a trail of clothes from the bathroom to where he's sitting - a shoe here, a sock there, another shoe, another sock, and finally - his shorts.

Me: Isaiah, where are your shorts?
Isaiah: Grandma, I told you yesterday I don't need them so I took them off. I'm not going anywhere.
Me: No, you did not tell me "yesterday" that you were taking them off. You can't sit around naked.
Isaiah: But Grandma, I not naked; I have on my shirt and unnerwear. I don't need shorts. I'm not going anywhere so I can just wear my unnerwear and shirt.

I think it must be inbred in boys to take off their clothes and sit around in their underwear. I don't think they outgrow it, either.