Being a girl and going to high school, any amount of gaming I do is considered 'hardcore' by others. But that definition is obviously..... dumb.
I don't like it when someone says that hardcore = FPS games, though. Just because I may not REALLY like any FPS games (other than SWB2, for obvious reasons), doesn't mean I don't love to sit back and drain my life away playing any of the FF games, or Resident Evil or something. Good grief, a 'hardcore gamer' is defined by how much they love the game and how much time they spend on it.
Gaming is someone's hobby, and being a 'hardcore gamer' is left up to them to decide on. They can be a 'hardcore' Mario fanatic or Farmville and so on. So don't be hating on the people who don't spend all their game time on FPS games.

RPG and strategy games are pretty fun too.