My son and him sagging his pants?

My son is 16 years old an athlete straight A student and a great kid. The only problem is he sags his pants, not mega low like to his knees just maybe about half way down his butt, he's not a gangster or anything like that, he wears normal jeans or shorts and normal shirts. Lately though, I have been telling him to pull up his pants, and he pulls them up really far up like Urkel which he knows I hate that show, so now when he walks around the house he does that just to make me mad and give in. When his friends come over I would always tell them to pull up their pants to, so guess what they started doing as well. So now Im at the point where I am just going to let them all sag their pants. Any opinions or tips would be greatly appreciated. And again theyre all great kids, they are just trying to mess with me