The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) describes NPD as possessing at least five of the following nine criteria.
A grandiose sense of self-importance
Preoccupation with fantasies of unlimited success, power, brilliance, beauty, or ideal love
Believing that they are "special" and unique and can only be understood by, or should associate with, other special or high-status people (or institutions)
Requiring excessive admiration
A sense of entitlement (unreasonable expectations of especially favorable treatment or automatic compliance with their expectations)
Being interpersonally exploitative (taking advantage of others to achieve their own ends)
Lacking empathy (unwilling to recognize or identify with the feelings and needs of others)
Often being envious of others or believing that others are envious of them
Showing arrogant, haughty behaviors or attitudes
Just about every movie bad guy--and every real-life bad guy (a least the public figure-types)--meet NPD criteria. Which has horrible consequences, but makes the disorder easier to identify when it comes to the exam!