The phrase comes from everyday French slang, where je m'en branle is a vulgar, emphatic way of saying I really do not care. Shortened with a casual bah at the start, it became a handy reaction clip shared on soundboards, in WhatsApp audios and in short video edits. Its popularity is less about a single source and more about its usefulness, as one short line instantly signals total indifference. French-speaking creators reuse it for arguments, chores, school and work jokes where a shrug is the whole answer.