The only thing better than Justin Timberlake and Jimmy Fallon being real-life besties is Justin Timberlake and Jimmy Fallon being fake summer camp besties.

The stars reverted back to their pseudo '97 sleepaway camp personas on 'The Tonight Show' last night (Dec. 16), mischievously disobeying their counselor's orders and shamelessly belting out Third Eye Blind's 'Jumper' every chance they got.

In addition to showing off their vocal talent -- seriously, even as dorky, braces-clad teens Justin and Jimmy could still harmonize with the best of 'em -- the guys also played a hilarious game of Truth or Dare, where JT confessed he has a crush on 'Full House's' Kimmy Gibbler.

And as it just so happened, Andrea Barber -- who portrayed Kimmy on the family-friendly sitcom -- was watching.

"Ditto, @jtimberlake. Ditto," she later tweeted, heart eye emoji and all. LOL!

Check out Justin Timberlake and Jimmy Fallon as summer besties in the video above!

Old-School! See Justin Timberlake + More Celebs' Yearbook Photos

More From Hot 107.9