Ronda Rousey

Among so many mistakes, this latest one might be the biggest for Justin Bieber. Turns out the singer had a harsh exchange with Ronda Rousey that has the UFC fighter calling him out in the media.

In a video interview with Cosmopolitan, Rousey recalls how Bieber offended her and upset her little sister when the pair tried to get a picture with him.

"I walked over there, and I said, 'Excuse me.' And he turned to me [and] goes, 'I've already taken a billion pictures today, OK?'" Rousey says. "And I said, 'Yeah, but,' … and he goes, 'A billion,' and walks off. And totally snubbed my little sister. And then she looks at me, and she's on the verge of tears, and she goes, 'I'm no longer a Belieber.'

"Yeah, I don't think I'd want to hang out with him. I'm not a Belieber. I was, but I'm not anymore."

Rousey isn't sure what motivated Bieber to be so rude, but there's a decent chance it's got something to do with her ongoing feud with Floyd Mayweather. Bieber and Mayweather have a close, well-documented relationship -- Bieber has even joined Mayweather for training sessions in the past.

Bieber also attended Mayweather's fight against Manny Pacquiao earlier this year and made an appearance in his locker room before the fight.

Rousey, meanwhile, has been one of Mayweather's most outspoken critics of his domestic violence record. She's made pointed remarks to the media insulting his intelligence and prowess as a fighter.

Last May, Rousey dismissed the idea of fighting Mayweather, saying, "I don't think me and him would ever fight, unless we ended up dating."

So there's bad blood there, and maybe Bieber is staying loyal to his buddy. Either way, he just lost a couple fans -- and made an enemy out of one of the hottest athletes in the world right now.

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