He'd told Neal -- he'd told him -- that if he made a move towards the original Matisse while they were waiting for the forensics guys, Peter would handcuff him. He guessed Neal hadn't believed him. Or couldn't pass up the chance. He'd moved, and Peter had grabbed him, pushed him face-first against the wall, crowded into his space to keep him there, and pulled his arms back. Neal hadn't fought (but when had Neal ever fought? More a lover than a fighter, more a charmer than a bruiser, always.) And he wasn't resisting now that Peter was turning Neal's arm (to reduce the play that might allow him to slip the cuff) and tightening the second cuff behind Neal's back.
It's like that med student thing. Peter had heard that just about all medical students think they have whatever horrible thing they're studying at the time. Eventual age and experience teach them that no, almost all of them are healthy young adults who don't have to worry about anything until after they turn 35. But until then, the medical students fixate -- that was the word he was looking for. In law enforcement, there are also some common fixations, that mostly dissipate with age and experience. With cops, the fixations get sexual, god alone knows why.
He can't say that he was ever particularly excited by restraints, himself. He and Elizabeth tried it and enjoyed it, but that had more to do with him and Elizabeth playing, than an actual kink. After a while the cuffs were retired as sex toys.
Given Neal's history (arrested twice, imprisoned for years, and fitted with an ankle restraint), Peter wouldn't have expected him to have a restraint fetish. But the evidence in front of him said otherwise. Neal's color was high, his breath short, and he was squirming against Peter. Not a panic attack, the way Peter had thought at first. Nope. Neal was one turned-on felon, crushed between Peter and the brick wall, with his hands twisting and testing the grip of the cuffs on his wrists.
So Peter asked, growling in his ear, still holding Neal against the wall. "You have a thing for restraints, Caffrey?"
Neal shook his head "no", then tilted it back, exposing his throat, almost leaning his head onto Peter's shoulder. "It's not the cuffs," he said, "it's the company."