Then you're going to LIVE for this video!!!
She's gone undercover -- and she OWNS it!
Ch-ch-check out the video for Birthday here (above)!
Hook up alert?!?!
But she did find a HIGHlarious way into the pic because she ended up making a video spoofing the Biebs' Brazilian bedmate who recently filmed him sleeping.
During a visit to Capitol FM Breakfast, Mileybird got down in the vid that guest-starred the Biebs and her tongue - of course!
Ch-ch-check out Mileybird's laugh at the Biebs (above)!!!