To expose one’s private affairs in public, particularly any unsavory family secrets. This metaphor is a French proverb that became famous when Napoleon used it in a speech before the French Assembly upon his return from exile in Elba in 1815. It was picked up by numerous English writers, among them Trollope, who wrote (The Last Chronicle of Barset, 1867), “There is nothing, I think, so bad as washing one’s dirty linen in public.”