What is 9+10=21 meme?

The 9+10=21 meme originated from a vine video that went viral in 2014. In the video, a young boy is asked what 9 plus 10 equals, to which he confidently responds, "21." The video became popular due to the boy's humorous and incorrect answer, spawning remixes, parodies, and internet jokes. The phrase "9+10=21" was often used as a punchline or inside joke online.