Put it at the end of a failed attempt, after the setup and the visible mistake, then follow it with Hello Darkness My Old Friend if you want the moment to linger, or a short laugh if you want the next scene to start lighter.
About this sound
This 4.7-second clip is a muted trombone sliding down in a slow, droopy wah-wah-wah-waaaah, with the final note stretched out for extra effect. It feels instantly deflating and funny, like the air leaving a proud moment, and it turns a small flop into a clear, shared joke without a single word.