I agree that it's odd to feel "dishonest" to sit quietly through a prayer if you're not Christian. My feelings about prayer vary from day to day, as do my feelings about religion. Still, all humans need to eat, regardless of their religious orientation. If a family observes a moment to say grace, let them. My understanding is that one person's spoken prayer covers everyone in the room, so unless you're volunteered to say the prayer, you're good to go. If it's a silent moment of thanks, just reflect on how nice it is to have food to eat and friends to eat it with. No big whoop.