L’esprit d’escalier, a phrase coined in the 18th century by Denis Diderot, means, in literal translation, staircase wit. It denotes those missed opportunities for a dazzling riposte, a charming bit of repartee, that occur too late—only, as it were, on the staircase as one is departing. Everyone surely has had this regrettable experience.

Well perhaps not everyone. Oscar Wilde, entering America for his 1882 lecture tour supposedly told the customs agent: “I have nothing to declare but my genius.” When a chorus girl held open...