To summarize a lengthy and not particularly interesting story, I'm nearing the end of a friendship with someone who's a bit of a twat. In retrospect, her behavior is pretty spot on with the "red flags" that a variety of internet articles on the subject had warned me about. Those being: manipulating people (usually with appeals to emotions), forcing the friendship to move quickly, badmouthing others behind their backs, controlling others, disrespecting others' boundaries, etc. Basically, I keep her at arm's length, but we both hang out in the same circle of friends, so I have the opportunity to observe the same questionable behavior now aimed at other people. From this perspective, it's been kinda interesting in a "watching a train wreck" sorta way.

And I've been wondering some things. What exactly compels people to behave this way towards their supposed friends? Are they aware that they're doing it? She doesn't even try this behavior with me anymore, but she still does it to others fairly regularly. How would you handle this sort of behavior? How would you handle it if you witnessed it being aimed at another friend? How ought we address this behavior?

I don't know. I'm just looking for a good discussion on the topic.