The meme stems from NSYNC's 2000 smash hit "It's Gonna Be Me." When singing the titular line in the song, Timberlake annunciates the word "me" as "May." According to a 2016 article from E!

We hope we never have to say "Bye Bye Bye" to this meme. It's May 1, so, of course, members of the boy band *NSYNC acknowledged what has now become a time-honored tradition: the "It's Gonna Be May ...