Esprit de l’escalier (French): a witty remark that occurs to you too late, literally on the way down the stairs … (Wikipedia)
More often than not, a witty (or wicked) remark does come to mind right away – never mind esprit de l’escalier – but remains unspoken because I am too polite (or sometimes too scared) to utter my first thought.
During my teen years, I felt obliged to subject my ‘ready wit’ to eternal vigilance – lest I inject a constant stream of more-or-less subtle obscenity into ordinary conversation.
These days, the voice in my head is as inventive as ever.
I could comment right here, right now … but … but I am too polite to say what I’m thinking.