Narcissism is one of those disorders that the public has taken to their hearts and calling someone a narcissist is a common insult to attack someone perceived as vain, egocentric or self-absorbed, however this does not reflect the full spectrum of the diagnosis. As with most things the public presses to their heart as the pejorative du jour, they failed to understand the full complexity of the disorder and the diagnostic criteria. Being a vain, self-centered bastard is part of the diagnosis, but is not the only thing required to be a narcissist, if it was most of us would qualify at one point or another.
Narcissism in the western culture is a growth industry  thus, the socio-cultural aspects of the diagnosis, is influenced. This follows from the BPS response to the DSM-V, where they write
The putative diagnoses presented in DSM-V are clearly based largely on social norms, with ‘symptoms’ that all rely on subjective judgements, with little confirmatory physical ‘signs’ or evidence of biological causation. The criteria are not value-free, but rather reflect current normative social expectations. Many researchers have pointed out that psychiatric diagnoses are plagued by problems ofreliability, validity, prognostic value, and co-morbidity. 
Thus with a growing level of narcissism within culture, and thus social norms, how long until today’s narcissist is tomorrow’s normal person? Furthermore, considering the growth of social media, how does a diagnosis of being grandiose and self-centered work with a culture where most women can have a cadre of online admirers constantly validating and complimenting them?
Incentive theory is a subset of research on “human motivation” or as I like to call how “How to dangle the carrot and wave the stick around“. For instance, if you’re running a sales office, and you need more sales, what is more effective? Bonuses or threats of people being fired? It comes from a field of psychology made famous and pioneered by B.F. Skinner who did a lot of work on operant conditioning. Those of you who read my post on expectancy theory and equity theory are already partially familiar with this concept and some of its effects.
Sometimes such incentives can have positive effects, such as when you offer a major bonus to the best salesperson. Sometimes they can have very unfortunate effects when the encourage hiring patterns that focus highly on “social fit” and less on ability, education or experience. Sometimes it can have positive effects, such as seeing a quarterback getting laid like a rockstar and that encouraging young boys to try to be good at football. Other times it can have negative effects, such as when a “nice guy” notices that all the guys he knows with girlfriends like to tool them up once in a while and decides that in order to get a girlfriend he has to become the type of guy who tools up women.
A core principle of incentive theory is that people do what you are encouraging them to do in order to reach their goals. If a man wants to get laid like a rockstar, he will adopt the behaviors that make that happen. The 2008 financial crisis is interesting in this respect, in that the system encouraged the very behavior and recruited personalities prone to such behavior, that almost lead to a systemic collapse.