My DH really has no idea about decent table manners. I'm not pretending mine are impeccable, but I'd say they are pretty good. I don't believe it is his fault, as his family are all worse than he is (probably because they haven't been subject to 10 years of nagging from me). Christmas dinner round the PIL is like a bunch of pigs around a trough. DH didn't even know, until I told him, that you are supposed to put your knife and fork together when you've finished eating.
In a nutshell, what I'm saying is that his disgusting table manners are his parents fault. I am very anxious that history doesn't repeat itself.
So, any ideas on how I go about instructing our DC about table manners without using DH as an example of how not to do it, as they are bound to eventually notice that he doesn't do what I tell them to do.