Justin Bieber snubbed the WRONG WOMAN ... refusing to take a picture with Ronda Rousey's little sister -- so says Ronda who claims Bieber was super rude about the rejection.
Ronda says it all went down at the Cannes Film Festival in 2014 -- where Ronda and her 16-year-old sister say they saw Bieber at a media event and approached him for a photo.
Ronda tells Cosmopolitan.com she thought Bieber would be open to the pic since they were all at a media event and "everyone's taking pictures today."
But what ensured, according to Rousey, was pure snubbery ... and clearly, Ronda still holds a grudge.
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