The voice belongs to Flapjack, the wide-eyed kid from Cartoon Network's animated series The Marvelous Misadventures of Flapjack, which aired from 2008 to 2010. In the show's Spanish-language dub, the drawn-out 'mentirosooo' plays as an exaggerated accusation of lying, matching the series' rubbery, over-the-top humor. Short reaction lines like this one circulate widely as meme audios in Spanish- and Portuguese-speaking communities, where the single-word punchline fits WhatsApp jokes, TikTok dubs and gaming clips without needing any setup.