At first I just thought you meant just dicks. Like people who figured out that if you can take advantage of people's natural tendency to be submissive to authority--which you can give yourself by just taking charge--you can use people to your ends. Those people you are best to avoid as much as possible or like was said, show them that you won't submit, that you are on to them, it's a whole power struggle thing. I'd still rather not deal with them though, they seem a big waste of time and are totally untrustworthy, so if I can identify them I avoid them. The harder stuff is where it's layers of dishonesty about being vampires, where they don't see what they are but somehow still operate the same way.
Just general negativity or the whole perpetual victim thing is really draining in a different way, they are like anchors that just want to take down as many people as they can. There is no way to convince them that they are making things the way they are. Nothing can ever be good enough, there's no point where their needs are satisfied. I got caught in all that with a girlfriend too and although it never changed my outlook too much, I would have been much better off if I wasn't dealing with that siphoning constantly. At the time I didn't realise how futile it was to try and help her. I've known friends like this too, but they have less effect because I don't really have to tolerate their whining if I don't feel like it.
