Acting childish

When the children were young and now with our grandchildren, I now see that ADD may be playing a part in an activity that was irritating to me but I didn't know what it was.  Now I am seeing that he acts like a child when he is with children.  He is the roughest, loudest, most baby-talkish of the group.  He squeels and giggles and things ALWAYS get out of hand with someone ending up crying.  Then H stomps off saying it wasn't his fault and that I am crazy for being concerned.  I must decide each time how much I can tolerate.  How much I should expose my grandchildren to and when to tell him he is being inappropriate.  There are enough kids here to be kids with each other.  What the family needs is a model to follow, not a teaser/clown.  I had an uncle who was like this and frankly I was afraid of that uncle....too teasy.  I can't seem to talk to H about this without his being offended.  But then I guess he will just have to be offended because when there are children around, he becomes a beligerent child. I know it must not feel good when someone tells you that you are not acting appropriately but if it was me, I know that I would listen and consider if maybe I should make some changes.  But H never alters and clings to his right to act the way he wants to.