Place it right after the gross reveal in a reaction edit, then follow it with Eww Brother Eww for a second reaction, or open with Oh My God Wow before the reveal so the first reaction sets up the payoff.
Über diesen Sound
This is a short human groan, just under two seconds long, with one drawn-out 'eugh' delivered in a flat, revolted voice. It lands as instant disgust, the sound of recoiling from something slimy, stale or badly judged, and it works because the reaction is blunt and unmistakable.