When: August 2009

In 2009, on the heels of her hit single "Bubbly", California girl Colbie Caillat was rumored to have hooked up with the Hollywood playboy. As they're both singer-songwriters with a similar laid-back vibe, it's entirely possible that, just maybe, they were together discussing a future collaboration. But as it's now 2012 and no such duet has surfaced, we're of the opinion that any beautiful music made here wasn't done in a studio, but between the sheets.

Smash Probability: If you're a gambler, and we are, one thing is certain: Much like you should always double down on 11 in blackjack, you should never bet against a John Mayer hook-up.