Filed under "things too stupid to believe but too entertaining to dismiss," Justin Bieber is alleged to have hooked up with Rihanna early in his relationship with Selena Gomez.

You know, back when he was a minor.

Statutory Rihpist, anyone?

Life & Style says that following a Lakers game on Feb. 20, 2011 (pictured above), Biebs and RiRi flirted up a storm and that he basically slam dunked her in the sack. Right.

Still, a "pal" of Selena's says, “It has devastated her. It really cut like a knife because it happened in February of 2011, when Selena and Justin had been dating for months and were falling in love. It’s caused Selena to question their entire relationship.”

Bieber and Gomez have been off and on for months, and the mag reports that Gomez is calling it off for good this time ... even though they were spotted together this past weekend.

“Selena thinks maybe they've been hooking up all along,” the source said. The source added that Bieber, who's pals with Rihanna's boyfriend and beater Chris Brown, got bizzy with the oft-naked fellow ganja enthusiast at the Victoria's Secret fashion show.

“During breaks, they’d sneak away to the Hotel Giraffe,” the source insisted. “They were alone — their security made sure of it. Hotel staff blocked off the entire floor for them.”

Or, you know, because they're famous and don't want peasants bothering them in general.

Though Bieber and Rihanna's camps scoffed at the allegations -- because, well, they're laughable -- Life & Style stands by its reporting, with its "source" urging us to believe that “Justin would never admit to it; he would never tell anyone he messed around with Rihanna.”

Maybe that's because he didn't want to incur Brown's wrath. Or maybe it's because the story is just utter and complete BS.