There's a difference between politeness and etiquette:
Politeness: chew with you mouth closed, reasonably sized bites, don't talk with your mouth full, keep your face clean, don't slurp your soup, etc.. Some of these change based on context (go to The Excalibur in Vegas and see a tourney. Full dinner, no silverware), but for the most part these are things that have a function reason and directly impact other people.
Etiquette: Eat off the back of your fork, eat peas with a knife, fork on the left/spoon, knife on the right, that fork for this, this fork for that, etc. etc.. This is all nonsense that people use to try and seem better than other people, and changes regionally (often in contradictory ways). It's stupid. Unless you need to impress someone (or you think you're better than other people when you're not), don't worry about it.
Point of interest, the "better" my etiquette, the more I'm saying the people I'm with are shallow, arrogant twits.
