I just heard.
Maybe I'm the last to know, but Michael J. Fox was originally offered the role of Duckie in Pretty In Pink. Scenes from that movie (one of my FAVES, by the way!) are still running through my mind with the Alex P. Keaton cut-out head placed on top of Jon Cryer's body - I mean, c'mon! Can you seriously picture Michael J. Fox doing anything during the 80's besides Back To The Future and Family Ties? Okay, okay. I didn't forget Teen Wolf. Unfortunately.
What would have happened to Jon Cryer had Michael J. Fox actually played Duckie? Well, I looked up Jon Cryer's resume on IMDB and found that he has been in lots of movies I've never heard of! But he probably wouldn't have even had those roles if he didn't get the Duckie role. And Two and a Half Men would be...what? It wouldn't be.
And Jon Cryer was also given the opportunity to audition as Chandler Bing in Friends. Thank goodness Matthew Perry took the role instead. I could never stand Chandler.