Danny DeVito Improv-ed One of ‘It’s Always Sunny in Philadelphia’s Funniest Moments, Rob McElhenney Says

It’s Always Sunny in Philadelphia co-creators Rob McElhenney, Charlie Day and Glenn Howerton possess the kind of prodigious talent that extends well beyond the small screen. Case in point: They too, can produce groovy disco tracks capable of keeping an entire club — or more importantly, Danny DeVito’s Frank Reynolds — dancing all night long. 

In the series’ early days, the trio briefly shifted their influences from the Marx Brothers to Donna Summer, penning an original disco song for Season Two’s “Mac Bangs Dennis’ Mom,” an instant Sunny classic inspired by none other than DeVito’s improv skills. 

“We’re on set that day, in the scene where Frank and Mac go to the discotheque to meet some ladies,” McElhenney explained during an episode of The Always Sunny Podcast. In the script, Frank had a “very specific move that he’s dancing to,” but DeVito decided to find a groove all to his own, providing his own tunes during the otherwise-silent dance sequence.

“At one point — this is not scripted — he goes back onto the dance floor and says, ‘Hey, ladies. I’m Frank,’” McElhenney remembered. “And then he goes, ‘Goooo, go for it, go for it!' He starts doing the move and singing, ‘Go for it!’”

At first, the It’s Always Sunny overlords were confused by DeVito’s singing. “We were like, ‘What the fuck is he doing?’” Howerton recalled. But some time later, they came around, finding DeVito’s improv-ed tune so hilarious that they decided to craft a new track specifically for the scene. 

Using an existing disco song as inspiration, the new song featured Howerton and McElhenney’s vocal talents — “That’s actually us, that’s me singing!” the Wrexham A.F.C. co-owner interjected — a fact that left Day feeling green(man) with envy. “I was very jealous that when we went to go do the recording of that, I had left for my honeymoon,” Day explained of the song. “I would’ve liked to have sung ‘go for it!’ as well.”