The only thing my ultra-conservative father and grandfather managed to do to me was to never ever let them anywhere near their grandchildren.
I also might've let my father know how it feels to get thrown through a bookshelf by someone a lot stronger when I got old enough to do so. Suddenly he was a lot less enthusiastic about physical violence. I wonder why. He still managed to fuck up my spine for life when he did the same to me - when I was 12. Took me 6 years and a lot of physio but he'll never hurt anyone else ever again.