Beam Me Up, Scotty!: There's no proof that she ever said the quote "if you can't handle me at my worst, then you sure as hell don't deserve me at my best", that is often attributed to her on the Internet.
What Could Have Been: Something's Got To Give, her last film project. While the studio did find a replacement actress after personal problems forced Monroe to quit, the entire production was canceled after she died.
She and DiMaggio were in the middle of repairing their relationship when she died, and if she'd lived they could have remarried. This is one of the many reasons why some people don't believe she committed suicide.