Put it at the very end of a fail sequence, after the setup has played out, then follow it with Awkward Crickets Sound Effect for the embarrassed aftermath. For a bigger reaction, lead in with Shocking Sound Effect just before the reveal, then let this clip close the joke.
About this sound
This 4.8-second clip takes a single fart noise and runs it through heavy bass boosting, so the low end rumbles and hits like a tiny explosion rather than a quick cartoon toot. It feels deliberately dumb, loud and absurd, turning a childish gag into an over-the-top punchline for fails, awkward pauses and sudden reveals.