It's usually coupled with another interest, as in, "I'm a huge Doctor Who nerd" or "Game of Thrones geek." This sounds nit-picky, but it's extremely important in this context because the whole idea of being a nerd is that you belong to a very small group of social outcasts. We weren't nerds because we enjoyed Star Wars -- you know, the highest grossing sci-fi film in the history of movies -- we were nerds because we were a small, annoying group of people who obsessed about it and knew every ridiculous, obscure detail of shit that didn't even appear on screen. We obsessed to a fault ... so much so that we couldn't connect with "normal" fans because our enthusiasm ruined the subject for them.
Don't even get us started on Han shooting second.
In other words, we aren't nerds because of our fucking hobbies or taste in entertainment. Yes, we tend to like things like comic book characters and science fiction movies ... but then again, so does every other person on the damn planet. And that's how non-nerds define their interests: "I'm a huge video game geek!" No, we're nerds because of who we are as people. And because the very definition of "nerd" is "socially inept," we cannot be included in the group when it becomes mainstream, as it has now. It's almost a paradox. A big, stupid, annoying paradox devoid of friendship and love.