Justin Bieber apparently got on the bad side of UFC champ Ronda Rousey because Floyd Mayweather's BFF almost made her sister cry.

As recounted by the undefeated champ to Cosmopolitan, she took her sister to the Cannes Film Festival earlier this year and they saw Justin Bieber taking some pictures with fans, and her sister got suddenly excited.

"My little sister is very hard to impress so she really doesn't care about anybody," she said.

"Do you think he'd want to take a picture with me, you'd think he'd want to?" UFC champ quoted her sister as saying.

So UFC champ Ronda Rousey approached Justin Bieber who apparently didn't recognized her and curtly said, "I've already taken a billion pictures today."

"Yeah, but she's the only 16 years old at the whole party, you know?" Ronda Rousey begged Justin Bieber.

 "A BILLION."

And that's the end of the conversation.

"She looks up to me and on the verge of tears, she says, 'I'm no longer a Belieber,'" she said.

Ronda Rousey also added, "I'm not a Belieber. I was, but I'm not anymore."

But Justin Bieber still got off easy as Ronda Rousey has not really declared that she's going to beat the "What Do You Mean" singer, unlike his BFF Floyd Mayweather whom the UFC champ insisted she's going to beat.

During the Reddit AMA, Ronda Rousey's fan asked if the UFC champ can beat Floyd Mayweather.

Ronda Rousey responded, "Floyd is one of the best boxers of all time. He would definitely beat me in a boxing match. I unfortunately don't get into 'matches.' I fight for a living. In a no rules fight, I believe I can beat anyone on this planet. Boxing is a sweet science with strict rules that I respect very much and aspire every day to improve at. But you said ruleless fight, and that's my honest answer."

Ronda Rousey has been taking jabs at Floyd Mayweather and during the 2015 ESPYs, the UFC champ told reporters, "I wonder how Floyd feels being beat by a woman for once. I'd like to see him pretend to not know who I am now."