Perhaps he was being a little more than cocky, not to mention the gleaming smugness of his smile as he leaned back in his chair, not caring that his left hand was cuffed. This state was just crawling with wickedness, and at first, he really didn't want to get so many notes in his already extensive dossier.
But your sweet face and stern look, with those slender fingers resting on the side of the gun barrel? Mm, tempting. The thing was, of course, that this clever head probably knew more than it could say—not that he didn't trust the cops for nothing, right? At least that's what he'd told Sam when he'd voluntarily turned himself in at the police station. Omitting the flirting part.
"Don't you think it's weird, Dean Winchester, that all the weird stuff happens around you?" you say, setting a glass of coffee (bitter—he wouldn't count on favor) on the table in front of him. "And now you come and voluntarily surrender yourself to the police. And for what?"
Dean smiles, looking you over from head to toe without hesitation—there's nothing criminal about enjoying the view. The job would be too boring if every city didn't have at least one female face to bare his charms with. For information purposes, of course.
"Oh sweetie, trust me, those eyes would make any woman..." he pauses for a moment, taking a sip of hot coffee, almost wrinkling his nose. "... willing to do a lot of things. They're very partial to talented male hands—you know, I've killed the undead more than once, and from the look in your eyes, you know exactly what I'm talking about."
Bingo. A meaningful silence, the hum of the dim lamp above you, and the faint creak of the wooden chair beneath him—that's all that remains in a small room where there is nothing but brute insolence and skilled workers at their craft.
"I'm sorry for your loss of your father—a terrible death even for a hunter. Looks like we're both working on the same case, and after this... how about we go on a date?"