Place it right after the unbelievable claim, before any wider reaction, so it reads as the first response. Follow it with Oh My God Wow to build on that claim, then Damn to close the exchange with a final word.
Über diesen Sound
This is a very short reaction clip lasting 0.47 seconds, built around the single word 'boy'. It gives a flat, unimpressed feeling, as if the speaker has heard enough and has nothing more to add. Its brevity makes it easy to drop into a reply without slowing the moment down.