Place it right after the unbelievable claim in an edit, then follow it with a Bruh sound for disbelief and an Oh My God meme sound to close the reaction, keeping the sequence short so the oath stays the punchline.
Over dit geluid
This is a single spoken 'walahii' lasting just over a second, delivered as a quick, emphatic exclamation. It feels funny and slightly dramatic, making a bold claim sound bigger and a doubtful moment feel theatrical, which is why it works so well as a reaction when plain words do not carry the disbelief.