I have more friends than you: Narcissism can be revealed in one's facebook page.

Researchers at the University of Georgia have found that certain characteristics of one's Facebook page can reveal one's narcissism. Narcissistic personality disorder is a collection of personality traits in an individual including shameless self-promotion, selfishness, and deception all under an charming veneer. They tend to have shallow relationships but with many people, and have, according to the DSM-IV TR, "a pervasive pattern of grandiosity, need for admiration, and a lack of empathy."

From the article:

The researchers found that the number of Facebook friends and wallposts that individuals have on their profile pages correlates with narcissism. Buffardi said this is consistent with how narcissists behave in the real-world, with numerous yet shallow relationships. Narcissists are also more likely to choose glamorous, self-promoting pictures for their main profile photos, she said, while others are more likely to use snapshots.