In my experience the people I've seen self-label this way (in a non-anonymous way) do so because they think it reflects well upon them (it's 'cool', demonstrates intelligence or superiority, etc.). It is usually the limit of their self awareness and they are never outwardly conflicted. My inner arm-chair psychologist thinks it stems from varying combinations of insecurity and lack of empathy.

Seems like more of a British thing. They're also IMHO more willing to take an honest ribbing over screw-ups without getting all pissy. They take it and dish it out.