Place it at the peak of a mock attack, right before the impact lands, then follow it with an anime punch sound effect to sell the hit and close the gag before cutting away.
About this sound
This is a four-second burst of repeated piu piu noises that sound like tiny cartoon laser shots or finger guns in action. The effect is light and rapid rather than powerful. It gives a listener a silly, upbeat feeling, turning a small gesture into an exaggerated, playful attack that lands as a joke instead of anything serious.