With fast food and lots of casual eating, a good many people have never been taught any table etiquette. And for eating junk food in a fast food joint, I think it's a little outre to require everyone to eat like they're at the Waldorf Astoria, but I do think it is ok to insist your kids don't do anything at MacDonald's that makes you want to hurl.
The proper time to put your napkin in your lap is when you sit down at the table.
When you leave the table, you fold it neatly on the table where your plate was.
Some rules of etiquette are meant to just make eating less hurl worthy for the others at the table. Other rules are meant to make it easy for a waitress to quickly clean up and bus your table. Other rules are actually for hygeine - keeping used napkins away from other people's plates, etc.
Waiting for the host or hostess was just meant to show the host respect and thanks for providing the food.
Ewesheep, if your daughter is 'stabbing' her meat with a fork fist, well, what I do is I tell the kid that we do not eat like cannibals in this house and if you want to eat, you have to eat it in a way that doesn't make the cook want to hurl, and that is the end of that.