\ess-preed-less-kah-lyay\
We’ve all been in a situation when we think of the perfect thing to say in response to something provocative or insulting too late to say it in the moment. When the right words come, the right time is past. The French call this too-late inspiration l’esprit de l’escalierplay . Esprit is the root of our word spirit, but in French can also mean “wit,” so this phrase is translated literally as “wit of the staircase” and is used to mean repartee thought of too late, on the way home.
The expression was coined by Denis Diderot, the French philosopher of the 1700s, so we can imagine that the grand staircase of a château or manor is what he had in mind.
Is Will Smith experiencing l’esprit de l’escalier after Slapgate?: Oscar night incident provides teachable moment on the value of ‘staircase wit’
— (headline) Irish Times (Dublin, IR), 31 Mar. 2022