Place it at the exact reveal, then follow it with Oh My God Wow when the reaction needs to grow, and keep Damn Meme Sound nearby for a second reply in the same thread. Use Sudden Suspense before it to set up the moment it answers.
Über diesen Sound
This is a short, under-two-second vocal reaction built around one stretched word, 'damnnn,' delivered with slow, disbelieving emphasis. It lands as amused shock, the sound of someone caught between laughing and shaking their head at something unbelievable, impressive, or badly timed.