Don’t tell them but the French didn’t in fact invent etiquette
When dining in France, it is considered rude to finish the bread before the main course has been served, and ruder still to slice the bread with a knife, lest the crumbs land in a lady’s décolletage. In China, you should never place your chopsticks upright in a bowl of rice, and in Bangladesh you may eat with your fingers, but should avoid getting sauce above the knuckles. If you are guilty of any of the above, may I direct you, politely, to a new documentary on the World Service. The programme takes aim at many outdated traditions (including those that resign women to the kitchen), but the conversation is
