Place it at the reaction beat after the reveal, not under the build-up. Lead in with the dun dun dun sound button for the fake-serious set-up, then follow this clip with the spongebob fail sound button if the moment collapses into an embarrassed mess afterward.
About this sound
This 2.6-second clip is an exaggerated giggle that builds into a full super laugh, pitched to sound both silly and a little scary. It feels gleefully unhinged, turning a normal reaction into something funny and unsettling at once, like someone laughing at the exact moment they should be screaming instead.