The truth of the matter is that most people have some of these qualities and the ones who deny it the most are usually the worst.
I read a book on this subject called Emotional Vampires - Dealing with people who drain you dry...
It's not the best read in the world, the author is a bit of a ranter. The info is good enough though.
The proper term for an "Emotional Vampire" is called a Personality Disorder and like I said, most of us have these traits.
The worst of them are totally hypnotised by their egos though...
If you have ever met such a person you will know how amazingly hypocritical their actions can be and that they really have no idea how insane they are!
My Dad is one of these people and I can tell you now, if you have never had to deal with one, then you don't know how lucky you are! Or maybe it is the other way around hehe
It was said that "they" are more likely to go after people with a lower vibration freq, I believe this is true.
*** The main weapon they use is called ""Psychological Projection"", look it up, interesting stuff.
It was also mentioned that the more you mimic their energy the more it will affect you and add fuel to the fire, which is also very true.
Therefore awareness is your primary defence, for the most part.