Cam Newton
Losing a Super Bowl is one of the most devastating feelings for an elite football player. They dream of becoming franchise icons and receiving a ring that immortalizes their achievement. The Panthers had a golden opportunity to break their duck against the Broncos in 2016. But they suffered a heartbreaking loss and it hurt badly (via SBNation).

Their star quarterback, Newton, walked off the field without shaking hands with his opponents. There was a slight media agenda against the reigning MVP but it was still bad sportsmanship. In hindsight, most people agree that it was forgivable because of the wild emotions. Peyton Manning famously did the same thing after the Colts lost against the Saints.