Adam turns to his friend Bryan on graduation day and tells him that he will pay Bryan $100 if he sings "Despacito" to the entire graduating class when he walks across the stage.  A few moments before Bryan goes onstage, Adam turns to Bryan and says "changed my mind, deal's off".  Bryan ignores Adam, goes onstage and sings to the entire class.  He hops off the stage and asks Adam for the $100, which Adam refuses.  If Bryan were to sue Adam, who would win and why?