"I forgot that's what gets you all hot and bothered, Jace, girls killing things."
"I like anyone killing things, especially me." he said with a smile.

"Each man kills the things he loves". I recognise that in myself, in relationships, even with guitars, beautiful things that I've had and wilfully destroyed.

"Can I help you with something?"
Clary turned instant traitor against her gender. "Those girls on the other side of the car are staring at you."
Jace assumed an air of mellow gratification. "Of course they are," he said, "I am stunningly attractive."

Was it weird hearing from Jace? I mean, since you found out . . ."
"Yes? Since I found out what? That he's a killer transvestite who molests cats?"
"No wonder that cat of his hates everyone.

"I figured all your classes were stuff like Slaughter 101 and Beheading for Beginners."
Jace flipped a page. "Very funny, Fray."

Then again, it was Jace. He'd pick a fight with a Mack truck if the urge took him.

Jace hadn't seemed perturbed, but knowing him, Simon had no doubt he could kill several people in a single morning and go out for waffles afterward.

Even in half demon hunter clothes, Clary thought, he looked like the kind of boy who'd come over your house to pick you up for a date and be polite to your parents and nice to your pets.
Jace on the other hand, looked like the kind of boy who'd come over your house and burn it down just for kicks.

He also wanted to destroy something, everything, perhaps himself.

Master Kosta...What a pleasure! Selendri tells me you’ve expressed an interest in getting killed.

I loved killing bad guys.

I didn't," said Jace. "At least, I didn't finish it. It's Magnus Bane." He grinned at Alec mockingly. "Rhymes with 'overcareful pain in the ass.'

"Sebastian just smiled. “I could hear your heart beating,” he said softly. “When you were watching me with Valentine. Did it bother you?”
“That you seem to be dating my dad?” Jace shrugged. "You’re a little young for him, to be honest.”
“What?” For the first time since Jace had met him, Sebastian seemed flabbergasted.

What makes you think that Valentine's change of plans had anything to do with your brother?"
"Because only Jace can piss someone off that much.