An 'x2k' is a needy, power-hungry mess of a human being, one obsessed with being at the centre of anything and everything. Holding a party? They'll want to take over organising it. Buying stuff? You can bet they'll have spent twice as much as that by the next time you speak. Having a shit? They'll squat down on the floor next to you and coil off a monster.
Roald Dahl's book, The Twits, says that people who are ugly inside are ugly outside. This is true of the x2k. You'll see them on every street. They're the ones with curved spines and deformed faces.
"Hey, this is my party. Don't be such an x2k."
"This would've been done five hours ago if you weren't such a fucking x2k."
"Bollocks, I've just trod in a big pile of x2k."