You know you're a nerd when you're cool and nobody else understands.
Indeed
The Lich King
Kyouzou replies:
The what?
Then he says this: You know you're a nerd, when you find your self playing Maple Story/Runescape/World of Warcraft etc.
Fail
You know you're a nerd when you're not good at explaining something.
Or you're a nerd when you avoid nerds because that makes you [N]ot [E]ven [R]emotely [D]orky, aha!
You know when you're a nerd when you call someone @$5\\/\\/!|D£ and not asswipe (sorry for language). Oh and you're also a nerd when you type everything correctly (and quite quickly) like this.
You know you're a nerd when you make a 3-D model of a Roman Atrium with wall paintings, statues, and all when a teacher asks you to make a simple floor plan of a Roman house room.
You know you're a nerd when you find yourself ranting on AG forums while listening to Ben Folds Five
You know you're a nerd when instead of hanging with your friends you're spending time building your museum-quality Viking boat instead.
You know you're a nerd when you try to be an acrobatic ninja and end up kneeing yourself in the face.