Daymond John's -- UBER-MISTAKE ... I Blew a Billion Dollar Deal!!!

You know what SUCKS?? Having a chance to invest in an $18 BILLION COMPANY ... but making the WRONG decision ... just ask "Shark Tank" star Daymond John.

John -- who's usually pretty damn good when it comes to investing -- admits he was offered the opportunity to own a piece of Uber ... and turned it down!!!

Hey, even the greats can't bat 1,000 ... but John admits he still thinks about the numbers ... and what his bank account COULDA been -- had he pulled the trigger.