5. Dexter Jackson, Super Bowl 37
The Tampa Bay Buccaneers defense dominated Super Bowl XXXVII. Someone on the defensive side of the ball definitely should have won the MVP. Dexter Jackson wasn't a terrible choice. Some would argue there are better choices, but Jackson did intercept Rich Gannon twice. He was the leader of the best offense in the league, and the Bucs made him look silly.
Whether Jackson was the right choice is not the point here. Jackson's career took a turn after the Super Bowl. He immediately became a free agent after winning the Super Bowl. He agreed to sign with the Pittsburgh Steelers, but he rescinded that agreement and signed with the Arizona Cardinals. Because of that decision, the Steelers drafted Troy Polamalu. It worked out pretty well for them.
Meanwhile, the Cardinals stint only lasted a short time despite signing a five year, $14 million deal in 2002. A bulging disc really derailed his career. After it happened in the 2004 offseason, he never returned to the Cardinals. He was cut in October, and he eventually returned to the Bucs.
Jackson would play for the Bengals before ending his career in the UFL. He had a ton of promise, and he was legitimately good in his Super Bowl performance, but the rest of his career left a ton to be desired.