Here is the golden rule of manners, says Sandi Toksvig: “Do naught unto others what would cause pain if done to you.” That is absolutely useless as a guide to manners, and not just because of the weird “what”. Ask someone who chews with his mouth open if he is doing aught that would cause pain if done to him and he wouldn’t have the foggiest awareness of any such thing.It is the impossibility of always realising when we are offending that makes us blush with shame in retrospect at some unintended bêtise.In a way, Sandi Toksvig is a comfortingly old-fashioned guide to manners. She couches her advice chiefly in the imperative, like the Victorian book of manners called Don’t. “Don’t rush,” she says. “Don’t put your feet