Narcissists think of themselves as special; chosen; beyond the fray — rules do not generally apply to them, but oh do they ever to you. They tend to see the world in black and white terms, as a Manichaean struggle of hierarchy vs. fairness, with strict social status to abide by and perpetuate — a world of dominance and submission, with themselves at the top.
The higher on the Cluster B scale you go (with psychopathy at the top), the less empathy these individuals possess. Without empathy, there is no basis for forming a conscience. One could say the classic defining hallmark of this group of personality disorders is that the people exhibiting narcissism have little to no conscience.
Part of the dark triad along with psychopathy and Machiavellianism, narcissism is characterized by manipulative behavior towards others and a malevolent, often exploitational approach to interpersonal relationships.
You could say that narcissists are those who never manage to find enough escape velocity to get outside themselves. They stay stuck forever in an infantile loop of getting what they want, using people along the way to achieve their goals. Narcissists think transactionally, and are always seeking to maximize benefit to themselves, at the expense of others if necessary or possible.
See also: word salad