What is emo,hardcore,metal? in terms of lyrics....

[Eido]

I am writing a song, and I am stuck on the lyrics.
What kind of song subjects should I work on if I want to write Rock/Hardcore/Metal music? How far can you go with love lyrics before people call you an emo?

I am a total newbie on writing lyrics....

Thanks people :)

[KillaBink]

Just write. You're already limiting yourself before you even get started.