esprit de l'escalier [ es-pree duh le-skahl-yey ]
1. a perfect comeback or witty remark that one frustratingly comes up with only when the moment for doing so has passed: Writers, by nature, tend to be people in whom l' esprit de l'escalier is a recurrent experience.
Origin: First recorded in 1905–10; literally, “wit of the staircase” (i.e., after one has left the gathering)
Now YOU come up with a sentence (or fic? or graphic?) that best illustrates the word.