the honesty of a five year old

So i'm hanging out with Grant today, who spends a lot of time with his hands down his pants. Usually I just politely remind him that it's not very polite to talk to someone with your hands down your pants, and he stops.

Well today it's really quite exessive so I say, "Hey Grant, what's the deal with your pants, get your hand out of there."

And he replies, "Well my penis just keeps wobblin' and wobblin' so I have to touch it all the time just to keep it in its place!"

How do I respond to that?