Bill Belichick and Eric Mangini
Bill Belichick isn't exactly known for being warm and fuzzy, but he is a winner, and he seems to inspire gratitude from his players and staff. So it came as a shock to the sports world when, in 2007, Eric Mangini, a former assistant on three Super Bowl winning teams coached by Belichick, leaked that Bill would videotape opposing teams in an attempt to decipher signals, which is illegal under NFL rules.
As a result, the Patriots were fined and lost a first round draft pick in 2008. Mangini must have been teased a lot or something—maybe he refused to cut the sleeves off his hoodie, and Bill never let it go. Mangini has since said he wishes he could take "Spygate" back; no comment on the hoodie.