What to say
You find yourself standing next to a royal in the loos - applying lipstick next to Kate, or washing your hands next to Harry. What should you say? What should you definitely not say?
When you first meet them, call them "Your Royal Highness". After that, it's "Ma'am" or "Sir". (And remember: Ma'am rhymes with "jam".)
If you do meet Kate, say something safe, such as: "Wonderful coronation. I'm already looking forward to William's." Perhaps you should leave off that last bit.
If, after all that tea and champagne, you meet her in the loo again, don't say, "Back again? Dear, oh dear!"
Try not to say what comes naturally, which is to ask for a selfie and make fun of what everyone else is wearing. Instead, it would be good manners to show sympathy with the King. "The poor man must get so sweaty with that robe and the crown," you could say. "I bet he wishes he were Prince Andrew." No! This last bit would be tactless; it's true it was the King's brother who told us he doesn't sweat, as a result of experiences on active service as a pilot in the navy. But he shared the information when he was defending himself against claims of sexual misconduct.