Biggest Super Bowl blunder ever has gotta go to Young Jeezy ... for bailing on the Falcons at the start of overtime and crowning them champs ... before the GREATEST. COMEBACK. EVER.
Jeezy and his crew were leaving NRG Stadium with the game tied 28-28 ... but despite relinquishing a 25 point lead, the rapper's confident as hell ATL's bringing home the Lombardi Trophy.
Check it out ... Jeezy's even got a parade date in mind.