Narcissistic personality disorder (NPD) is a long-term pattern of abnormal behavior characterized by exaggerated feelings of self-importance, an excessive need for admiration, and a lack of understanding of others' feelings. People affected by it often spend a lot of time thinking about achieving power or success, or about their appearance. They often take advantage of the people around them. The behavior typically begins by early adulthood, and occurs across a variety of situations. The cause of narcissistic personality disorder is unknown. It is a personality disorder classified within cluster...