"Yet!" For Mat, it's an important distinction. He hasn't killed anyone yet. But the potential is there. It's inescapable and undeniable. Why can't Jesper understand that?

It hurts as much as anything else, feeling like Jesper isn't listening to him. Or worse, dismissing his fears and the very real danger here.

"Fuck's sake, they won't punish me. And if I do get in any trouble, it's sure as hell not my fault. I'm not the one who painted a target on me!" Anger has long been a defense mechanism, and it's rising hot and quick now. If Jesper loves him so damn much, he has a pretty fucked up way of showing it.

"Just calm down, would you? In case you failed to notice, I can protect myself. And Light knows you have plenty of other pretty young things to keep your real bed from being empty so I'm sure my absence in it won't be that noticed! This really isn't the crisis you've decided it is."

A low blow, and Mat knows it. But he's too upset to care right now. Jesper's emotional displays somehow only make him more upset, a twist of sick guilt spurring him to further reaches of anger.