Put it just before the twist is shown, then follow the reveal with the Vine Boom Sound Effect for extra impact, or lead into it from the SpongeBob Fail Sound Effect when a blunder sets up the exposure.
About this sound
This is a brief orchestral sting of three low, heavy notes followed by a longer, sinking final note, lasting just under five seconds. It feels tense and funny at once, turning a small slip or obvious twist into a moment of dawning realisation. It comes from The Simpsons, where such exaggerated reveal cues were used to parody serious television drama.