Whatever studies tell about NPD, it can be easily recognizable.

From what I have read online, these are some common interpretations and findings that can be kept under the symptoms.

-Have an unreasonably high sense of self-importance and require constant, excessive admiration.

-Feel that they deserve privileges and special treatment.

-Expect to be recognized as superior even without achievements.

-Make achievements and talents seem more significant than they are.

-Be preoccupied with fantasies about success, power, brilliance, beauty or the perfect mate.

-Believe they are superior to others and can only spend time with or be understood by equally unique people.

-Be critical of and look down on people they feel unnecessary.

-Expect special favours and other people to do what they want without questioning them.

-Take advantage of others to get what they want.

-Have an inability or unwillingness to recognize the needs and feelings of others.

-Be envious of others and believe others envy them.

-Behave arrogantly, brag a lot and come across as conceited.

-Insist on having the best of everything — for instance, the best car or office.