False memories need to be cultivated, constantly ‘watered’ to persist. Telling as many people as possible the gross details of sexual abuse, which a normal person would not do, is a clear flag.
Why is this stranger telling you these things?
The Victim of False Memory must push these fallacies in the front of their minds so as to not lose them.
Trying to argue, reason, poke holes in the story is a waste of time.
Getting away from the Victim is the wisest. If enough people walk away as the story begins, the Victim will cease to have an audience and might learn to stop the blather.
If the blather can be stopped or at least limited, this means less ‘watering’ of the False Memory. The less it is watered, the weaker it becomes.