Technically in the USA: It is impolite to begin eating without first washing your hands, rest your elbows on the table, chew with your mouth open, double dip in

Technically in the USA: It is impolite to begin eating without first washing your hands, rest your elbows on the table, chew with your mouth open, double dip in shared dishes, leave your napkin on the table, and also all sorts of rules about which spoon to use when. None of these rules are followed by your average American and nobody really cares, I imagine it's similar to these.