The phrase is everyday German, most associated with southern German and Austrian speech, where jo works as an emphatic yes and spinnst is a colloquial way to say someone is talking nonsense. As a standalone clip it circulates on soundboards as a compact reaction, detached from any single show or creator. Its appeal online comes from that familiarity for German speakers and its expressive sound for everyone else. Short dialect reactions like this travel well in chats, edits and streams because they convey teasing disbelief faster than a written reply.