That perks his attention, the simple fact that Stiles has clearly given at least some amount of thought to this, been thinking about him like that. The mix of to how the teen slides fingers into his briefs is intoxicating. The way fingers curl around Derek's erection, and he gasps lowly at the heat of the touch. And then he's talking, and Derek would candidly admit that half the time he thinks Stiles talks too much, but right now he doesn't want him to stop.

He quickens the pace of his fingers a little encouragingly, leaning in as Stiles talks about riding him, and then he's talking about fucking Derek and there's a shiver that runs visibly through his shoulders. His green eyes watching Stiles, lingering on his mouth that's damp from his tongue, and there's a slow nod at that implied question. "Yes. Yeah, I want that," his voice is rough, shaky with desire as he looks into the teen's warm brown eyes.

He trusts him, somehow.