At the risk of being Captain Obvious, playing games as a hobby makes someone a gamer. My girlfriend plays a few iphone games and sims 3 but you could say she is a gamer to an extent (she reads a lot more and watches more films than playing games). Hardcore I'd only relate to the amount of time someone plays but enjoys anything. Someone who only plays WoW or final fantasy isn't hardcore, just a muppet.
One thing that does annoy me, think it was Ali and someone else who stated it, but folk who say 'play this console as it's a real games console, that one is just a toy'. Was stated in relation to the vita and 3ds/ds but quite commonly used against the wii also. If ones a toy because it plays games, so is the other one. Such a moronic outlook.
Either way, one person is not more or less of a gamer because of the console they play on, just as someone who owns all games consoles isn't more of a gamer than someone who owns 1. I'd more than happily play on any console/gaming device. I just chose xbox and pc as I use a pc anyways and xbox is more suited to my needs.
I'm sure S-smith and his wife Jboo would say I'm wrong but that's why they/he are pricks.
Some say he's half man, half fish. Others say its more of a 70/30 split. Whatever the percentage, he's one fishy bastard.