Justin Bieber is at war with late night TV hosts. After he bantered and verbally sparred with David Letterman over tattoos last night (June 21), JB locked horns with Jimmy Fallon.

In this clip, funnyman Fallon claims that he knows The Biebs' 'Believe' will sell more copies than his comedy album 'Blow Your Pants Off,' but insists he can beat him at a ton of other stuff, to which The Biebs asks, "You want a piece of me?" and narrows his eyes. Fallon replies, "Bring it, Biebs," The teen says, "Suck it grandpa" and from that moment forward, its' on… like Donkey Kong.

It's actually almost literally on like Donkey Kong, since the two give each other the stink eye and then play video games, Laser Tag, Marco Polo and other childlike activities to see who can best whom. Oh, boys!

The frenemies engage in an epic battle of pushups, where youth and skill (The Biebs) seem to prevail.

They get a work out, and require a Capri Sun juice break so they can fuel up on sugar before diving right back into the thick of competition. They are going head to head in wrestling (with The Biebs putting Fallon in a headlock) and Fallon pulling out what he thinks is Rock, Paper, Scissors victory.

The sudden death dance off? Now that's where it's at. Take a look.

Watch Justin Bieber vs. Jimmy Fallon