Bruce Springsteen and 'Late Night' host Jimmy Fallon are pals, and whenever the Boss stops by Fallon's set for anything, you better believe he's performing ... And sometimes even Fallon takes the stage with him for some hilarious and quite unexpected cover performances.

Recently, Springsteen stopped by 'Late Night' in NYC to promote his new album 'Wrecking Ball,' and Fallon busted out his Neil Young impersonation as the two performed a duet to LMFAO's 'Sexy and I Know It.' Hearing Bruce Springsteen sing "wiggle, wiggle, wiggle, wiggle" in his signature, gravelly vocals is enough to make you split your side laughing.

Also, on an older episode of 'Late Night,' the Boss joined Fallon onstage to perform a cover of Willow's 'Whip My Hair,' with Fallon once again taking on the role of Neil Young. The duo gave the song a folky spin, yielding comedy genius as they croon about "turning their swag on."

So, out of the two pop covers that Bruce Springsteen and Jimmy Fallon (as Neil Young) have sung live on 'Late Night,' which is your favorite? Check our their renditions of LMFAO's 'Sexy and I Know It' and Willow's 'Whip My Hair' below and cast your vote!

Watch Bruce Springsteen + Jimmy Fallon Perform LMFAO's 'Sexy and I Know It'

Watch Bruce Springsteen + Jimmy Fallon Perform Willow's 'Whip My Hair'

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