Put it near the end of a reaction cut, after the reveal, and follow it with the Anime Ahh Sound Effect to stretch the joke. For a failed boast, open with the Awkward Moment Sound Effect, then let this clip answer it.
About this sound
This is a six-second burst of rapid, high-pitched giggling that starts with repeated hihi sounds and finishes on a light ahaha. The bright, anime-style voice sounds teasing and a little smug, turning a small joke or awkward reveal into something sillier. It gives the listener a cheeky, unserious lift, like a character laughing at a plan that just worked.