Put it right after the mistake is visible on screen, then follow it with the Oh No No No Laugh for a second reaction, or cut to the Shocked Meme Sound when the other person reacts. Keep it as the punchline, not the opener, so the fail sets it up.
About this sound
This five-second voice clip has one speaker call someone an idiot in a flat, taunting tone, then break into long, loud hahaha laughter that carries the rest of the sound. It feels mocking and gleefully mean-spirited, like a playground taunt aimed at a friend who just messed up, and the laugh makes the insult land harder than the words alone.