esprit de l'escalier
/eˌspriːdəleˈskæljeɪ,〈法〉ɛspʀidəlɛskalje/noun
mass noun
- used to refer to the fact that a witty remark or retort often comes to mind after the opportunity to make it has passed事后想到的妙语（或反驳的话）。
词源
French, literally 'wit of the staircase' （i.e. a witty remark coming to mind on the stairs leading away from a gathering）.