The first time he noticed them, Derek tripped. It was like the ground just suddenly fell away beneath his foot when he went to put it down, and the next thing he knew, Stiles was at his side, biting back a laugh, and asking if he was all right.
"Dude, you know that's my thing, right? Stop stealing my job. You: graceful werewolf; me: uncoordinated human. Let's leave it that way."
Derek barely noticed the words spilling from Stiles' mouth though, because Stiles was leaning down toward him. And while on any other day, that'd make his shirt gape in the front, this one was... It was tight. Too small. Thin from years of wear. And it did absolutely nothing to hide Stiles' nipples.
It was insane. He'd known Stiles for years, but this was the first time he'd noticed them.
After he picked himself up and walked away, waving off Stiles' concern, Derek actually sat down on the rail of his balcony to think about how it was he'd never noticed them. It wasn't like he never saw the guy. Stiles was always around.
But the more Derek thought about it, the more he realized Stiles never wore t-shirts. Or rather, he never just wore t-shirts. Even today, he'd been wearing a plaid shirt unbuttoned over his t-shirt. He'd only removed it when he'd spilled soda on the collar. And when he wasn't wearing t-shirts and plaid, he was wearing hoodies, or a jacket or some kind of layer.
For a wild moment, Derek was pissed. He felt as if he'd been lied to for the entire length of time he'd known Stiles. As if the entire pack had been keeping this life-altering secret from him.
When the anger threatened to overwhelm him, he did some deep breathing, meditative exercises, and put it from his mind.
At the next pack meeting, everything was back to normal. Stiles had covered up his frankly obscene nipples and was back in a ratty old hoodie, standing in front of the open refrigerator while he yelled insults at the rest of the pack.
Derek grunted in annoyance, thought about telling Stiles to get out of the way, and then... And then stopped. He considered the way the string of the hoodie looped up and into Stiles' mouth as he stared into the fridge. Derek let his eyes creep over the long, knobby-jointed fingers that wrapped around the outer edge of the fridge. And he made a decision.
Stepping forward, he curved his hand up under Stiles' raised arm, allowing the pads of his ring and pinky fingers to brush over where he knew Stiles' nipple to be, then exerted pressure. His fingers dug hard against the puffy flesh even as he turned the move into a friendly shoving match for the fridge.
But Stiles' heartbeat tripped, and his breath caught on a tiny, near-inaudible whine, and Derek knew.
Oh yeah. They were just as sensitive as they looked.
It didn't take much more than a raised eyebrow and a murmured suggestion to send Stiles tripping into his bed after that. It would have been flattering if Derek had thought it had anything to do with him specifically and not sex in general.
So here they were, Stiles naked on his bed, arms stretched up to grip the bottom of the headboard. His fucking pouty little nipples were on display for Derek alone and it was enough to make him press the heel of his hand hard against his dick.
"Fuck," he muttered, staring at them.
Stiles flushed and started to lower his arms when Derek let out a menacing growl. "I...I just..."
"Do you have any idea," Derek asked, crawling onto the bed and reaching to run his thumb over one pink nipple, "how fucking ridiculous these are? I want to spend hours..." His voice broke when Stiles arched his back, keening at the touch.
"Fuuuck," he repeated, then leaned down to bathe the other nipple with his tongue.
From the first touch, it was all bitten off curses and pleading whines. But Derek could not get enough. He pinched lightly, then harder. Scraped with human nails and teeth. Bit and sucked and laved until Stiles' nipples were stiff little peaks rising up from his chest, looking almost fucking feminine.
Derek bunched up the flesh under one in his hand as he took the nipple into his mouth, sucking until it was dark and bruised. Marked.
When the other matched, when Stiles' hips were rocking into the air with precome rolling down the length of his dick, when tears of frustration were leaking from the corners of his eyes, when his lips were bitten red, Derek stopped and sat up.
There was only one thing left to do.
"Look at me," he said, and waited for Stiles' unfocused eyes to clear. Well, as much as they could with tears still wetting the clumped together lashes.
"Good," he murmured, and then leaned back down, dragging his beard lightly over Stiles' tortured flesh.
The scream Stiles let out as he came, completely untouched, rang in Derek's ears for days.