The question pretty much says it all. I've been wrong about a ton of teams and players through the years, whether it was thinking Ohio State would roll Florida in 2007, the team would not get throttled by Iowa in 2017, Damon Arnette would not go in the first round of the NFL Draft, but you have to go all the way back to 2008 to find my true north of wrongness.
The New York Jets took Vernon Gholston with the 6th pick in the 2008 NFL Draft after his junior season saw him record 14 sacks as a Buckeye, including one on Michigan's Jake Long – who only gave up two sacks his entire career. Gholston rocked the NFL Combine, tying for first on the bench press and I'm thinking this guy is going to be a beast in the NFL.
Four uninspiring years later and he was essentially out of the league. Added bonus: Brian Hartline, taken in the fourth round a year after Gholston, had a much sturdier NFL career than I ever thought he would
I look forward to being even wronger than this someday.