There is something wrong with me, I realized.
I was reading David Mitchell's Ghostwritten (not really crazy about it, absorbing but not enjoyable), which opens with the narrative (spoiler alert!) of a cult-follower planning terrorism. He is looking into the faces of his victims and feels only exultation, not contrition.
But I let it go.
Why? Well, there is a back story. Unhappy kid, bullied, no one understands him, then a larger-than-life figure gives him all the attention and respect he has been craving his entire existence, and he imprints.
It's understandable how he became a monster. His family, his classmates, the world, failed him.
"To understand everything is to forgive everything," Frederick Forsyth wrote in The Phantom of Manhattan. Books and movies—good ones, at least—delve into the story of a character, through and through. People have reasons for what they do. While the action may be horrible, the perpetrator's motivations came from somewhere, however misguided and warped he may be.
When I comprehended this, I knew now how to achieve actual dan l'kaf zechus: Pretend the other is a book character. Consider the back story. Low self-esteem? Lack of childhood socialization? Currently dealing with a soul-crushing situation?
It doesn't excuse what she said or did to me, but it does humanize her, as opposed to she-devil-who-made-me-feel-like-crap.