You are a nerd if:

You get more upset when you die in-game, than when 1 of your relatives dies.

You are not a nerd if:

Someone calls you a lucky noob in-game, and you care only enough to respond "STFU NERD I PWNED YOU SO HARD ROFLZORZ" (this will normally provoke the 'NERD' to carry on with lame insults usually about your mom or attempt a fat joke...).