'We Can't Stop'
Miley Cyrus' Bangerz hit was originally written for Rihanna, Mike WiLL Made-It told MTV News. "Rihanna, she heard 'Pour It Up,' and then she got on 'Pour It Up' right away," Made-It explained. "And she didn't even hear 'We Can't Stop.'"
'Since U Been Gone'
Candidate for greatest song ever "Since U Been Gone" was apparently offered to Pink and Hilary Duff, both of whom passed on it, before coming down the ladder to Kelly Clarkson.
'I'm a Slave 4 U'
The Neptunes originally wanted Spears' sexy jam to go to Janet Jackson. Jackson demurred, and Spears' future with that snake at the VMAs was sealed forever.
'We Found Love'
Former Pussycat Doll Nicole Scherzinger was offered right of first refusal on "We Found Love," but said she was "busy at the time." She mentioned that she still has the demo of the song – maybe to punish herself? Her motivations are unclear.
Christina Milian (who has done some songwriting herself; she and TheDream wrote "Baby" for Justin Bieber) passed on "S.O.S." and the tune went to Rihanna. She hasn't released an album since, either caught up in her new life as a mom or just mourning the hit that got away.
'… Baby One More Time'
Max Martin initially offered this song to TLC for Fan Mail, and they turned him down, which ended up being fine for them: The album had the hits "No Scrubs" and "Unpretty" on it. Things worked out okay for Spears in the end, too.
Spears has really good luck with other people's leftovers. Written by team Bloodshy & Avant, with additional writing from Cathy Dennis and Henrik Jonback, "Toxic" was pitched by the foursome to Kylie Minogue, who ended up passing on it. "It's like the fish that got away," she said of the decision. "You just have to accept it."
'Whataya Want from Me'
Adam Lambert's biggest hit was written by P!nk, Max Martin and Shellback, before winding up in Lambert's hands. Pink clearly still felt for the song, recording her own version of it, but it's Lambert's version that lingers.