The phrase is everyday Brazilian slang, shortened in the title to c ta de brincadeira cmg the way it is typed in chats and game lobbies. Clips like this spread through WhatsApp groups, TikTok edits and Discord soundboards because the meaning is clear even from tone alone. Its short length makes it easy to spam as a reaction button, similar in use to other disbelief lines, and it has stayed popular for expressing mock outrage without needing any context or setup before it plays.