If someone did listen , even though he did not accept any of it -
He should try to re frame the story to explain it in a positive light.
If that won't work - wait until the speaker leaves & explain it to all of the others.
If he did believe it -
Work on disbelieve it & decide not to transgeress anymore. & confess to Hashem. Also go back to the speaker & change his feelings.
Now may be a good time for a gem of Torah study.
www.GemsofTorah.com