Put it at the very end of the edit, after the fail and the reaction have played out. Let Awkward Moment set up the tension first, then follow Womp Womp Fail Sound with this clip to close the sequence and leave the ending standing alone.
About this sound
This 10-second clip gives a meme edit a firm, unmistakable finish after a joke, a failed attempt or an unexpected twist. It feels funny and deliberately overblown, turning a simple cut into a moment where the humour peaks and the bit is done. People get the signal right away, so the ending feels complete rather than just stopping.