Place it right after the confusing reveal, then follow it with the awkward moment sound to let the joke settle before cutting to the next scene, or open with the WTF boom sound when the twist needs a stronger opening first.
About this sound
This is a roughly nine-second voice clip built around a single drawn-out, emphatic 'what' that lands like a stunned reaction. It feels abrupt and slightly dramatic, turning plain disbelief into a joke setup that viewers recognise instantly in short edits.