Remember when Avril Lavigne beat out Justin Bieber for the title of most famous Canadian? Miley Cyrus sure does, and she's jokingly pissed that she didn't land the No. 1 spot -- even though she's, um, not even Canadian. The 'Wrecking Ball' singer is so annoyed, in fact, that she hilariously duked it out with the reigning champ herself during her Bangerz Tour stop in Toronto last night (Mar. 31). 

In the profanity-filled Instagram vid, Cyrus (clad in a rainbow-striped pajama onesie, of course) is angrily muttering to herself while reading a handmade magazine declaring the 'Complicated' singer to be the most "famous, beautiful and popular in Canada."

"Oh hey, Miley," Lavigne says with a 'Mean Girls'-esque hair toss as she flounces into the room. Cyrus is immediately on her feet, ready to confront her.

"I may not be Canadian," Cyrus retorts with a snap of her fingers. "But I'm the most famous person in Canada," she says, letting loose a string of unprintable expletives. The claws are out!

The blonde pop stars then begin fighting and Cyrus even starts whacking Lavigne on the head.

But the best part about the vid is that the pop stars clearly planned the whole thing out to a T. Check out the fake magazine that Miley is reading at the beginning -- that's some serious arts & crafts right there. Peep the LOL-worthy Instagram video above!