Place it at the exact beat where a joke falls flat, right after the failed line and before any reaction shot, then follow it with a sad trombone sting to underline the flop or an awkward cricket chirp to stretch the embarrassment before the scene moves on.
About this sound
This is a very short, under-a-second fart noise made to work like a joke button, with a sudden, cheap-sounding burst that lands and stops almost immediately. It feels silly, crude and instantly funny, turning a straight face or a quiet beat into deliberate slapstick without needing any setup or explanation.