The phrase is French for saying that someone else's grandmother is the wolf, a playful inversion of the usual insult that calls the other person the wolf instead. In online use, it functions less like a quotation from a single show or film and more like a reusable comeback, passed around in short clips, memes and reaction edits where the humour comes from deflecting blame onto an unlikely suspect. Its appeal is the contrast between the polite family reference and the sly, fairy-tale accusation, which makes it easy to drop into arguments, games and playful roasts without needing any context.