Also seems to be common with inviduals with strong Venus/Pluto placements, i.e. Venus in Scorpio, Venus conjunct, square, trine, sextile, and oppose Pluto, Pluto in the 7th house.
And I'm not saying all people with this placement seem to have these tendencies. Just to be clear on that.
It's really interesting to read the medical reasonings behind narcissism. Not excusing the behavior just trying to understand it.
On narcissists, this from the website Sociopath World:
"I'm a sheep, I'm a sheep, I'm in the sheep club. The sheep are the best. Those wolves are terrible. You have to be a special sheep to be in the high-wool club like me. If you don't believe I'm a sheep then you are calling me a liar. I was only eating meat because my boss made me do it. I was howling at the moon because you made me angry. I have always been a sheep. You are paranoid, I don't have canine teeth. You are imagining it. I'm a sheep. I won best sheep of the year award. We have to be on the look out for SueTarget. She's a wolf in sheeps' clothing. I am the one that did all the work. SueTarget messed it all up. SueTargets's fur looks fake. I'm the biggest sheep so I should be the boss. I have every right to punish SueTarget and eat her. It will be good for her, and teach her a lesson. I'm not doing it for me, I'm doing it for the team. I have to be the enforcer here and eat bad sheeps to help keep society clean. I used to be a vegetarian but because all these lazy sheep won't do anything, I am forced into keeping order and forced into being the bad guy and have to do all the eating of sheep."
I have had this fantasy with some people that are strategic gossips about exposing their poison by provoking them into hitting me, in front of others, like the Dark Knight interrogation. Since they always maintain a squeaky clean image.
Probably a dangerous thing to do though. You have to be really verging on sociopathy in order to be able to take hits and not hit back.
They double down on their emotional abuse, that is unless you move away from them far enough.
They have no boundaries, but not in the same way a child has no boundaries. It's more that they like to dictate you, your personal space, and your comfort zone. You're not aloud to have your own comfort zone. You're not aloud to be free from their iron hand, it's all about control and domination!
I think based on what I have posted on this whole forum for years, I'm pretty sure most people can guess how I know all this. 
Throw a tantrum, put the blame on you.
They don't take responsibility for their actions what so ever, everyone else is to blame.