Justin Bieber viciously attacked the one person in his deposition who didn't have a dog in the fight ... the soft-spoken court reporter, who he essentially called a f***ing moron.
Justin sat for the 4 1/2 hour depo in connection with a lawsuit filed by a photog ... who claims Bieber ordered his bodyguard to beat him up.
During the depo, Justin was asked if Usher was instrumental in jump-starting his career. He answered faintly, "Yeah." The court reporter was having trouble hearing, so she asked him to speak up.
Justin hurled the f bomb at her. You just gotta hear it.