Woulda, Coulda, Shoulda

There's a wonderful expression in French, l'esprit d'escalier. It means "the wit of the staircase", thinking of something brilliant you might have said during a conversation – as you're leaving.

Its origins come from leaving the drawing room of a grand 18th-century house. (The drawing room, where guests were entertained, was on the first floor – thus Upstairs, Downstairs.)

The Germans have a word for it, too, of course: Treppenwitz, "stairs wit".

I found a funny site entirely devoted to people's stories of l'esprit d'escalier here.