The line comes from I Think You Should Leave with Tim Robinson, the Netflix sketch series that premiered in 2019 and was created by Tim Robinson and Zach Kanin. Its sketches are built around people who refuse to admit they are wrong, which made short voice clips from the show ideal for memes and reaction edits. This I'm joking backtrack spread through TikTok, Discord and soundboards as a shorthand for walking back a comment, and it stays popular because almost every online argument needs that exact escape hatch.