Now, I have only one Chopin prelude and his 1st Ballade in my head. The Ballade is too long (and serious) for a nice little "show off" piece and the Prelude is okay but even though it’s not a super easy piece, it sounds like it is. My goal for now is to memorize (re-memorize) several more pieces so I'm ready for the next time someone asks me to play. So, again, what do YOU play when you spontaneously play for friends or family?
Congratulation, that you have the 1st ballade in your head. It is something I am just working on, will take further long months to have it completely memorized, and even further long months to play it acceptable.
If you can play the ballade, I would play the ballade. It is not too serious. It is simply a great piece, in my opinion one of the greatest pieces ever written for piano.
Only a question: which prelude you have in your repertoire?
I think, it is good to have some repertoire pieces one can play from memory, in case that there is a piano anywhere so to be ready to play something.
In my case it is the Chopin Fantaisie Impromptus, Chopin Etude 25/1 and some Bach WTC1 pieces I can play from memory. Oh, and small doses of alcohol are not bad at all in my case for performing.
I know that a Bach fugue does normally nobody bring in ecstasy, especially if I play...
But Chopin is really appreciated, that is my experience.