Place it at the very end of a reaction segment, immediately after the boast or dare you want to answer. Follow it with Ba Dum Tss to underline the joke, or open with Oh Brother This Guy Stinks and let this clip deliver the final insult.
About this sound
This is a short spoken French insult, delivered in a blunt, confrontational voice that says “mes couilles sur ton nez.” The delivery makes it feel aggressive and ridiculous at once, like a deliberately crude comeback meant to shock rather than argue. Even without understanding the words, listeners catch the attitude, which is why it works as an abrupt, immature punchline.