he knows what you are saying is true he just cant take the criticism because he sees it as a reflection of his bad parenting.
Its not rocket science to get the kid to loose some weight just get him a bike and **** and get him into some sports. He WILL have a harder time during his teen years if hes fat and you are right about that.
Just like people will wild out on you if their kid is in the store and making a scene and you tell them to make their kid STFU, this guy cant handle the constructive criticism that he may be a bad parent in this one area.
I mean if you seen a door jam in his house that was busted and gave him advice on how to fix it he would probably thank you. But when it comes to kids people think that they have to be perfect parents or that parenting skills should all just come naturally or something.
Tell him to get the dick out of his ass and fix his fat kid.