This sound comes from TikTok creator Brian the Fangirl, built around a possessive fangirl joke in which BF from the Lingo show is claimed as hers and other fans are told to back off. The long reeee became its signature, making it easy to recognise even without the words, and it circulated through TikTok fan edits, furry and meme pages where jealous and overprotective reactions fit the joke. It has stayed in rotation because the anger is clearly performed rather than serious, so creators can reuse it for crushes, rivalries and fictional characters without it feeling mean.