x Core means, an emo, who is Clean and by that i mean :
ect... you get the idea
I'm So X core...I shit razor blades and piss blood?
The hardest and utmost degree of core; the most X-treme level of core attainable.
billy: So I was fucking this girl in a jacuzzi, and I was on it so hard I hit my face on the side and broke my tooth.
me: Shit dude...so did you finish?
billy: FUCK YEAH...*walks away like a badass*
me: Damn that guy is x core.
Malibu Rum is so X core.