If you see him gobbling up his food, say something in a joking way, like, "Whoa, buddy. I'm pretty sure it's already dead and can't get away!" A subtle way of getting him to notice his gross table antics is to eat at a restaurant with mirrors - be sure he faces one as he eats, so he can see what a pig he's being. If it's his people skills that need work, then try not to shame him in front of others. Point out his problems, whether it's failing to say "please" and "thank you," swearing profusely or not tipping a server, in private. He'll be more receptive to your comments when it's just the two of you discussing it. It's possible he wasn't raised to worry about those sorts of things and just needs a few pointers.