The line comes from The Legend of Korra, the animated sequel to Avatar: The Last Airbender, where the flamboyant inventor Varrick frequently orders his loyal assistant Zhu Li to do the thing, often without explaining what the thing actually is. That running joke made the phrase instantly recognisable to fans, and the shortest, punchiest delivery was lifted as a standalone meme clip. It spread through soundboards and short-form video edits, where its vagueness is part of the appeal, because it can be dropped over almost any moment of sudden action.