I always suffer from staircase wit after an argument.
staircase wit
idiomThe thinking of an idea or course of action too late to use it effectively, or the tendency to do so.
Origin
disputed originCalque of French esprit de l'escalier.
I thought of the perfect comeback while walking home, a classic case of staircase wit.
He stood in the doorway, paralyzed by staircase wit, realizing the brilliant rebuttal he should have delivered hours earlier during the heated debate.