Nelson's 'Ha-ha!' comes from The Simpsons, the long-running animated TV series that debuted in 1989. The line is associated with Nelson Muntz, the show's school bully, and became one of the most recognizable catchphrases in television comedy. Online, the clip spread through GIFs, YouTube edits and short meme videos as a quick way to signal mockery after a blunder. It still gets used because the laugh is brief, clear and instantly understood even without showing the character.