Place it immediately after the joke in your edit, following a Wrong Answer Game Show sting for the failed setup, then let Sad Violin play as the scene moves on so the reaction becomes the start of the next beat rather than the end of the clip.
このサウンドについて
This is a short French voice clip of someone saying 'C'est pas marrant' in a flat, unimpressed tone, lasting just over two seconds. The delivery is dry and dismissive rather than angry, which makes it land as a deadpan reaction to a bad joke. It feels awkward in the best way, like a straight-faced shut-down that stops the laughter without raising the tension.