The definition of a narcissist used to be "someone better-looking than you," just as the definition of an alcoholic used to be "someone who drinks the same amount as you whom you dislike."
But I think that's changed.
Now it's "someone with more Facebook updates than you" or "someone who has more Twitter followers than you do."
The recent announcement that they were removing Narcissistic Personality Disorder from the DSM IV Statistical Manual caused quite a stir. But narcissism is no longer a disease. It's a lifestyle.
(Thanks, Kristina)