Justin Bieber -- The Prank Master

11/26/2010 8:30 AM PST BY TMZ STAFF
Justin Bieber's opening act made the mistake of pranking him during their tour -- so The Biebs decided to take it up a notch, by pranking them while they performed. 

As the story goes, some group called Burnham decided to fill Mr. Bieber's tour bus bedroom up with plastic balls. Bieber collected all those balls and brought them all on stage in Toronto on Tuesday night ... and proceeded to pelt Burnham with them.

The Biebs never backs down from a prank war.