You could make "(HIS NAME) is a terrible father" show up in Google suggest when he Googles himself. Internet justice. Or you could walk away the bigger man.
Dads can suck. I built my dad's bitch of a wife a new website and ranked her for some pretty lucrative terms, for free, at my father's request. When it was all set up and ranking I emailed her the keys to the kingdom (passwords) and though she uses the site every day neither of them have even bothered to respond to that email. No acknowledgement, not even a "10-4" I haven't heard from them in three months. Something bad and unforeseen is going to happen to that site.