Here is the medical definition:
Narcissistic personality disorder
Last reviewed: November 14, 2010.
Narcissistic personality disorder is a condition in which people have an inflated sense of self-importance and an extreme preoccupation with themselves.
Causes, incidence, and risk factors
The causes of this disorder are unknown. An overly sensitive personality and parenting problems may affect the development of this disorder.
Symptoms
A person with narcissistic personality disorder may:
React to criticism with rage, shame, or humiliation
Take advantage of other people to achieve his or her own goals
Have excessive feelings of self-importance
Exaggerate achievements and talents
Be preoccupied with fantasies of success, power, beauty, intelligence, or ideal love
Have unreasonable expectations of favorable treatment
Need constant attention and admiration
Disregard the feelings of others, and have little ability to feel empathy
Have obsessive self-interest
Pursue mainly selfish goals
Just about everybody I know and/or work with have many of the signs. The higher the manager position the more the signs. We tell that some of our mangers are "legends in their own mind"