Who: Ryan Lochte
Olympics: London 2012

Leading the 4x100 freestyle relay by half a length with arguably the world's best swimmer on the anchor leg, the US team looked like it could cruise to victory. Then things took a turn for the worse for the Americans. Lochte, likely tired from a demanding Olympic schedule, was outdone by 20-year-old Frenchman Yannick Agnel by a full second, the US lost, and Michael Phelps was denied another gold medal. In one night, Lochte beat Phelps by beating him, and beat Phelps by losing with him.