The phrase comes from informal Indonesian internet slang, with mbiyen borrowed from Javanese for in the past and bgst used as a shortened, blunt swear word in casual online speech. On TikTok, short spoken clips like this travel through edits, duets and reaction videos rather than through a single film, song or television scene, so the exact original post is hard to pin down. Its staying power comes from its flexibility: the same line can sound nostalgic, teasing or self-mocking depending on the footage placed underneath it.