The line comes from ASDFMovie, the rapid-fire Flash-animated sketch series created by British YouTuber TomSka, which debuted on YouTube in 2008. The vacant-eyed kid who loves trains became one of the show's most quoted recurring gags, popping up across later episodes. As ASDFMovie clips were re-uploaded and remixed, the two-word non sequitur escaped into wider meme culture, becoming a staple reaction sound on TikTok edits, gaming montages and soundboard apps, where its randomness is the entire joke.