Put it immediately after the wild claim in your edit, as the reaction beat, then follow it with Bruh Meme for a second reaction or Fail Sound Meme when the plan actually falls apart.
Über diesen Sound
This is a short, roughly one-and-a-half-second spoken German line asking, in disbelief, whether someone has lost their mind. The blunt question feels funny and confrontational, with a teasing edge that makes the disbelief land clearly. It comes from the German comedy film Der Schuh des Manitu.