Lately I went looking for the origin of the word blurb. The short answer is that Gelett Burgess coined it in 1907, and the long answer is that the more I rummaged the more I found, and the more I found the more I wrote, so I’ve postponed posting my findings until I’ve reduced them to a digestible size.
In the meantime I offer you “tintiddle”, another word coined by Burgess (1866–1951), who was an American artist, writer, critic and humorist. In his book Burgess Unabridged: A New Dictionary of Words You Have Always Needed (scanned here; plain text here) he defined tintiddle as:
An imaginary conversation; wit coming too late.
Everyone seems to have moments when they think of a devastating line some minutes or hours or even months after the opportunity for its expression has passed. It is the perfect quip in all aspects but one: timing. Maybe this delayed wit occurred frequently to people descending stairs in 18th century France, because the French philosopher Denis Diderot (1713–1784) called it esprit de l’escalier – literally wit of the staircase – in his book Paradoxe sur le Comédien.
Freud mentioned it in The Interpretation of Dreams, while Emily Stolzenberg suggests that it may be “of greater consequence to the speaker’s pride than the listener’s pleasure”. The moment has passed but we imagine delivering the line anyway, to satisfy ourselves or to repair wounded pride.
The French idiom avoir l’esprit de l’escalier means to have the wit of the staircase, in other words to be a bit slow with repartee. If you’ve seen the French film Ridicule (1996), set in 18th century Versailles, you’ll remember the importance of swift comebacks to spare oneself social humiliation. Contemporary usage often drops this connotation; esprit de l’escalier now refers to a witticism too late for any situation, embarrassing or otherwise.
I have heard several people lament the lack of an equivalent term in English, but this lack is only apparent, for tintiddle is that term. You might prefer staircase wit, or even the German Treppenwitz, a calque from esprit de l’escalier. Some translate Diderot’s expression as “wit of the staircase”, but that suggests that the staircase itself is witty – or not, if meant ironically. You can’t be too careful with words.
EDIT: More on this from The King’s English by H. W. and F. G. Fowler:
The French have had the wit to pack into the words esprit d’escalier the common experience that one’s happiest retorts occur to one only when the chance of uttering them is gone, the door is closed, and one’s feet are on the staircase. That is well worth introducing to an English audience; the only question is whether it is of any use to translate it without explanation. No one will know what spirit of the staircase is who is not already familiar with esprit d’escalier; and even he who is may not recognize it in disguise, seeing that esprit does not mean spirit (which suggests a goblin lurking in the hall clock), but wit.