Put it in the middle of a short gag, after a confident setup and before the payoff lands, so it bridges the build-up and the result. Start with It Was At This Moment He Knew to frame the mistake, then let this clip carry the tumble, and finish with a fail sound for the landing.
Über diesen Sound
This is a slide whistle that sweeps upward and then slides straight back down over about two and a half seconds, with no voice or other instruments in the clip. It feels playful and deliberately silly, like a visual gag turned into sound, instantly signalling that something has gone wrong in a lighthearted way. It was created by Jimmy MacDonald for the Mickey Mouse cartoon The Dognapper, released in 1937.