Narcissistic personality disorder (NPD) is a personality disorder in which a person is excessively preoccupied with personal adequacy, power, prestige and vanity, mentally unable to see the destructive damage they are causing to themselves and others.It is a cluster B personality disorder.arcissistic personality disorder is characterized by an over-inflated sense of self-importance, as well as dramatic, emotional behavior that is in the same category as antisocial and borderline personality disorders.