Summarize this article:

Not everyone who displays narcissistic traits has narcissistic personality disorder. Some people are simply selfish and have big egos, so be careful about over-diagnosing.  In order for a person to be diagnosed with narcissistic personality disorder, symptoms must interfere with basic functioning in at least two of the following areas: cognition, affect, interpersonal functioning, or impulse control.  A professional diagnosis is needed to confirm whether a person has narcissistic personality disorder or just narcissistic traits. Borderline personality disorder is often confused with narcissistic personality disorder. The two share many of the same symptoms, so it's important to understand the subtle differences.  People with both disorders may display anger, but people with narcissistic personality disorder tend to display anger towards others, while people with borderline personality disorder tend to express anger towards themselves. People with borderline personality disorder may care more about other people's concerns and opinions than people with narcissistic personality disorder, although they are still unlikely to interact with others in a normal and healthy way. It is possible for one individual to have both narcissistic personality disorder and borderline personality disorder, which may further complicate the diagnosis. Antisocial personality disorder, also known as sociopathic personality disorder, is also commonly confused with narcissistic personality disorder because people with both disorders tend to display a general disregard for other people. There are, however, some symptoms that distinguish the two disorders from one another.  People with antisocial personality disorder tend to have a harder time controlling impulses than people with narcissistic personality disorder. As a result, they are often more aggressive and/or self-destructive. People with antisocial personality disorder also tend to be more intentionally manipulative and deceitful than people with narcissistic personality disorder.

Summary:
Distinguish narcissistic tendencies from a personality disorder. Consider the possibility of borderline personality disorder. Recognize the possibility of antisocial personality disorder.