The phrase bu ren shi is ordinary Mandarin for not recognising someone, and as a sound it circulates as a short reaction clip rather than a line tied to a well-known film or show. Its usefulness comes from that everyday meaning: the rejection is understood instantly when placed after a greeting or a claim of familiarity. Short-form creators favour clips under a second long because they can be dropped into edits without breaking pace. That clear meaning and abrupt delivery is why it remains a handy brush-off for memes and chat replies.