The Rapper: 50 Cent
The Bet: In October 2011, Fif bet Lady Gaga's social media advisor Matt Michelsen $1 million that he couldn't finish the Ironman World Championship in Hawaii as a way to try and motivate him to finish it.
The Result: Michelsen finished the Ironman race and—we're guessing/hoping—50 paid up. If not, he better holler at him now. Fif's clearly got at least an extra $500,000 laying around after last weekend.