Ain't Got Rhythm is a song from Phineas and Ferb that became popular with "You Reposted in the Wrong Neighborhood" meme. These are a set of memes involving edits that make the song faster.
Originally, Ain't Got Rhythm was a song made in a Season 1 episode of Phineas and Ferb called "Dude, we're getting the band back together". It got popular as a meme in January 2017, along with Bee Movie edits, by a YouTuber called ShonkyWonkyDonkey.