Dammit, I should have wrote this first.
As far as the meaning, It’s not really a “taste” or a “flavor,” though, it’s the lack of one. It’s a feeling.
It’s like when when you’re a kid, and it just starts to rain or snow, and you want to catch that raindrop or snowflake on your tongue. But every time you try, it misses, despite falling on your face, your nose, your eyelids, with the additional spice of shame. It’s both uplifting and frustrating.
As far as the actual flavor of the pronunciation of L’esprit de l’escalier, (for me at least) it starts out minty-fresh and quickly devolves into murky dark coffee.