Narcissistic Personality Disorder is defined by Mayo Clinic as a mental disorder in which people have an inflated sense of their own importance, a deep need for admiration, and a lack of empathy for others.

With an impatient urgency, the narcissist will go to any length to be the center of attention--the ruler of his kingdom. He creates a gravity that pulls others into an admiring orbit around him. To say that a narcissist can get on your nerves is an understatement; a true narcissist can damage your career or business and even your reputation.

Here are some things you should know about some of the various personae of a pathological narcissist, and tips on how to deal with them.

Discern the difference between egotism and true pathological narcissism.

The term is loosely bandied about a lot lately, so begin with understanding the true characteristics and tendencies of this personality disorder before you leap to any conclusions. While not intended for diagnosis, this Narcissistic Personality Quiz provided by can help you determine if your assessment of this person is correct. The quiz is designed to determine if you are a narcissist. However, you can apply it to the person you're trying to assess.

They look out only for their own best interest.

The classic narcissist may appear to be caring at times, going out of her way to do you a favor or help you along in a project, but don't be fooled. These individuals are watching out for their best interest only and will not hesitate to throw you under the bus if and when it serves them.

Do not expect a consistent pattern of kindness from the narcissist and be careful not to fall under their spell, since narcissists are very good at attracting admirers. They are likely to expect you to return favors ten-fold, so it's best to politely decline when they offer a favor or helping hand.

Avoid criticism.

A little-known fact about narcissists is that behind the mask of arrogant confidence lies a fragile self-esteem; these people are sensitive to the slightest criticism. Avoid faulting or blaming them for anything. Instead, talk about the implications of their actions indirectly by discussing the impact the problem has had on you, your feelings, or the business. Focus more on solutions than problems. I usually don't recommend an indirect approach, but with this personality type it is the best route to take.

Don't bore them with your stories and accomplishments.

Sadly, the narcissist has no interest in your goals and achievements. If you want to celebrate a win, take it elsewhere. Your words will fall on deaf ears and the conversation will quickly turn to his world, as he engages in grandiosity and self-praise.

Flatter them.

It may feel manipulative, but the power of praise is one of the few ways to tap into a narcissist's best performance at work. If you need her to work on a project, tell her why she is the best person for the job and offer her your attention before, during, and after its completion. If you are a co-worker involved in the same project, fully expect your partner to take all the credit. To avoid being overshadowed completely, you might update your manager along the way and make casual mention of your part in the assignment when appropriate.

Don't challenge their viewpoint.

While it may be difficult, do your best to not get triggered by a narcissist's know-it-all behavior. Since they regard themselves as superior to all, narcissists offer up a full plate of unsolicited advice with little to no follow through of their own. They may believe they know everything but fail to put the knowledge to good use.

Unless you have time to waste, your energy is better spent in a productive conversation, which you'll find elsewhere. Don't bother trying to correct this person, as your viewpoint is likely to fall on deaf ears. Avoid endorsing their viewpoints, because this individual will not think twice about drawing you into a third-party debate or argument as an avid supporter of their opinions and actions. Politely acknowledge their input, toss in a compliment for good measure, and get on with your day.

Is there an upside to narcissism? Psychologists say an optimal level of narcissism can be helpful in life. "People with healthy narcissism don't have to rely on others for affirmation," says Susan Krauss Whitbourne, professor of psychology at the University of Massachusetts Amherst. "They feel good enough about themselves that they don't have to be always testing the waters. That is beneficial for relationships, and what's good for relationships is good for our health."