First of all, I totally dig Chopin, so I'm guessing this is either a giant fluke or someone I know asked me this questions.
Fuck you either way.
The only important thing to know about Chopin is that he loved the cock. No, I'm just kidding. Actually I have no idea what Chopin liked to put between his lips. Maybe he did love the cock.
(He was friends with Schumann and Liszt, two other bad ass composers who happen to be dudes.)
Oh shit. He did have a failed relationship with a chick, and then a reported 'relationship' with author George Sand. Did I just stumble onto something?
Anyway, the most -
Oh holy shit. George Sand was actually a chick! What the fuck? This confusion over his sexual preference has become the predominant mystery of Chopin's life!
Short Answer: ...the one thing that everyone should know about Chopin.
Note: There was nothing very interesting about Chopin. He's what you would expect. Child prodigy, wrote great stuff, died too young. And there was no confusion over his sexuality, I'm just dumb.