The phrase is a colloquial French way of saying tell me this is not true, with the double pas giving it a spoken, emphatic rhythm rather than formal grammar. Short French reaction lines like this circulate widely on soundboards and in edited clips because they are instantly quotable and easy to reuse out of context. Its popularity comes from that versatility: the same clip can read as genuine shock, sarcastic denial or playful overreaction depending on the image placed before it, which keeps it useful far beyond its original context.