Chris3711 that's BS circulates as a short, user-generated reaction sound rather than a clip from a well-known film, show or song, and its appeal comes from that everyday, unscripted feel. The phrase itself is a common piece of internet slang for calling out something false or unbelievable, which is why it slots easily into reaction videos, memes and stream highlights without needing context. Because the line is only about a second long, creators can drop it in as a quick punchline, and its blunt, conversational tone has kept it useful whenever a new dubious claim starts doing the rounds online.