Definitely l'esprit de l'escalier myself, though not always in hindsight. However, a very good friend managed a cracker many years ago.

He was of the opinion that I was going to beat the cr@p out of him for messing with my girlfriend; I had actually decided that his friendship was of more value than hers and I was intending to tell him so. When I sat down opposite him in the pub, though, he did not wait to find out and ran.

In order to part the crowd, he yelled "Bomb Squad, coming through!" which worked. He reached the door just as someone was coming in and the door opened in his face. Blood everywhere, pouring from his nose, he turned to the pub, by now silent and watching agog and said "It's OK, folks, controlled explosion!"