I think it is the equivalent of saying "I'm maaaad me" ... you are not a geek if you can call yourself one...
....or if you know a bit more than the average Joe about popular culture like Terry Pratchet, The Simpsons or Dr Who ....
I think proper geekdom can only be achieved if the subject is not terribly well known or if you need to be very clever or if you are fully engrossed in it to the point of insanity.