Jack & Jack -- Upstaged By Matthew Espinosa During Airport Fan Crush (VIDEO)

Pop rap duo Jack and Jack were at the center of an insane scene at LAX -- hundreds of their 6 million social media followers flocked to the airport -- but much of the crowd was really obsessed ... with their famous friend.

You've gotta see the J&J fans losing their minds -- tears were shed as they made their way through the crazed pack of tweener girls. But the most surprising part is a majority of the girls were screaming for the Jacks' BFF ... a dude named Matthew Espinosa.

Matt's pretty popular in his own right -- over 4 million followers -- but based on this video ... it looks like he's coming for Jack and Jack's crown.

For the older set, this is like Beatlemania ... for Pete Best (Google it, young people).