Place it right after the questionable claim in your timeline, before any response shot. Follow it with a wrong answer game show sting for a verdict feel, or precede it with a huh sound to set up the disbelief.
Über diesen Sound
A short spoken clip of a voice saying I doubt it in under a second, delivered flat and unconvinced. It gives a dry, skeptical feeling, like a polite but firm refusal to believe what was just said, making a tall tale feel instantly deflated.