Awesome replies.
I was going more along the line of "people will show you who they are... so believe them."
My coffee house friend is an active alcoholic with a really diminsihed memory. For her to somehow bring up a resolved incident and make it active... . well thats on her. I don't need to get caught up or hung up in her reality (especially if it is skewed because of the prism she sees the world in).
No amount of discussion or logic or fact is ever gonna change her thought that there was only the one time there was a short change (which really wasn't a big deal)... . just like all she can talk about is the other "friend" she has who is an azzhat but she keeps letting him relate with her.
She actually probably really likes the drama - so either I can play a part in it, or just brush that off and know who I'm dealing with (and always bring the correct change... .

)
I likened this to being in a relationship with someone with a PD.
I don't mean to suggest that my coffee buddy is anyone I would "get involved" with in a romantic sense, but if you even apply that dynamic to a S/O it stands to reason that if you really allow yourself to know the person you are dealing with (and yourself), your boundaries are stronger and issues which may arise in dysfunctional relationships go bye bye (mostly because you won't put up with the non-sense).