Fair warning: sexy times. Age difference. Teacher/student relationship. And some consensual roughness.

He wasn't exactly a child, so it wasn't exactly illegal. Well, John wouldn't have gone to jail for it. But he might have lost his job. And it was still wrong. God it was so wrong.

John could barely concentrate on giving his lecture. Because Sherlock had sat right there, in the front row. He had on a tight black button-down. The numerous hickeys and the bite marks on his long neck stood out like splotches of paint against his creamy, pale skin. They were almost five days old and they still hadn't faded entirely. He didn't have on a scarf. Didn't bother even trying to cover it up.

The bastard just sat there, smiling.

John's mouth went a bit dry, as he tried to refocus on his spiel about valence.

But he remembered sucking every single bruise onto Sherlock's neck. He remembered the way the young man moaned and whined.

John remembered the wonderful wet heat of Sherlock's mouth around his cock and he had to take a sip of tea out of his thermos before he could talk again.

Time slipped by agonizingly. John felt flustered. Discombobulated. Students kept asking questions, and he fumbled through the answers. He should have called in sick. God he'd been so stupid. Sleeping with a student when they were only five weeks into the semester. He'd have to deal with this until Christmas!

"All right, read chapter thirteen and fifteen for next week, and finish the accompanying workbook problems. I'll see you on Monday," John grimaced.

The students groaned and shuffled, rushing to pack up their things and get out to the weekend. They technically still had five minutes of class left, but John couldn't go any longer. He slumped behind his desk as the students filed out until there was nobody left but Sherlock.

"Did you have a question, Mr. Holmes?" John cleared his throat.

"Yes, professor," Sherlock slid out of his seat. Slow. Graceful. Like a dancer. All long limbs and muscle…

John shook himself. He stayed seated. Sherlock didn't stop in front of John's desk. No. He walked around it. Leaned against the edge of it right next to John. Too close for comfort. Almost touching. John rolled his chair away slightly.

"Um, yes?" He snapped. "What?"

"I'm doing a study on contusions. How fast they fade on different parts of the body. I've been monitoring these," he waved at his neck vaguely, "but I need a wider data pool. In a variety of locations. I think I need your help."

"Look, Mr. Holmes… what happened last week it was… it was a mistake." John couldn't look him in the eyes. He kept his head down. Shuffling papers. Looking busy.

"Oh come now, John," Sherlock drawled the name long and sinful. "I think the appropriate time to have moral objections was before you shoved me onto my knees and fucked my throat."

"Keep your voice down," John hissed. True, the building tended to empty fairly quickly at around three o'clock. That space between the afternoon and the night classes. But the university's halls always had somebody in them. And if the wrong person heard that sort of thing…

"Do you find me attractive?" Sherlock asked in a smoother, quieter voice.

"That's obviously not the issue at hand here—it's—you're too young."

"I'm nineteen."

"And I'm thirty seven! That's almost a twenty-year difference. Besides. I'm your teacher. This isn't… god. I should have never let this happen. I'm sorry, Sherlock. I really am. But I can't let this continue. Once was bad enough… "

Sherlock simply raised his eyebrows. He flicked out his tongue and ran it slowly over his plump lower lip.

"I won't tell anybody," he all but purred.

"That doesn't make it less wrong."

"We're both consenting adults. I like older men. You like me. You're inventing problems when there aren't any. You have a couch in your office, don't you?"

"I… why?"

"I'd like you to fuck me on it."

"No, Sherlock. You want to get me fired?"

"Well then let's go back your place. Or your car. Or a public park. I'm really not that picky."

"Did you miss the part where I said this couldn't happen again?"

Sherlock rolled his eyes. He leaned down until he and John were almost nose-to-nose. John could feel the younger man's breath on his face. It was dizzying. Intoxicating.

"Go on," Sherlock whispered. "It's really this simple. Take what you want."

Before John could think about it, he closed the distance. Pressed his lips against Sherlock's. Traced the seam of them with his tongue. Sherlock opened his mouth. Pliant. Submissive.

He tasted like cigarettes.

John tangled his fingers in those soft, dark curls. Flicked his tongue into Sherlock's mouth. Slow. Deep. How he'd like to fuck him…

Sherlock moaned into John's mouth. But he pulled back. Just for a second, to slide down onto his knees.

"Sherlock—we can't—"

The younger man pressed his face against John's crotch. Against John's rapidly hardening prick. Nothing but two layers of fabric separating them. Oh fuck. Oh Jesus.

"My office," John yelped.

Sherlock smiled. Bastard. That's what he'd wanted the whole time, wasn't it? They both stood up. A bit unsteadily. John gathered his things and they walked down the hallway together. It probably looked normal enough. Just a teacher and a student. Headed for office hours.

John's heart still raced.

He had a private office, thank god. At the end of the science hall. Frosted glass window. Door that locked. He ushered Sherlock inside and bolted the door behind them. He dropped his papers on the desk. He and Sherlock stared at each other silently for a few seconds.

Then John closed the distance. Wrapped his arms around the younger man's slender waist and started kissing him again. Feverish. Desperate. He walked backwards. The backs of his calves hit the couch. He sat. Sherlock slid down onto his knees again. Crowded up between John's thighs.

Sherlock had quick fingers. He unbuckled John's belt and unzipped his trousers effortlessly. He pushed down the waistband of John's pants, freeing his cock.

No hesitation. No time for thought. Sherlock leaned forward and parted his lips. He slid the head of John's prick into his mouth.

John bit down on his lip to suppress a groan. He rested his hands on Sherlock's head. A gentle weight. Not forcing him to take more. Not yet.

Sherlock swirled his tongue, pressed it against the sensitive underside of the glans. He didn't waste any time. He wrapped a hand around the base of John's cock and sank down onto him as far as he could.

John didn't want to wonder about how many pricks Sherlock had sucked before. Didn't want to wonder where he'd gotten the practice to be able to take a cock so well.

But the tip of John's erection hit the back of Sherlock's throat. The younger man swallowed, causing his muscles to contract wonderfully. The pleasure skittered across John's nerve endings. He found it difficult to worry about anything. Difficult to think.

He bucked his hips upward. And involuntary motion. But Sherlock went slack. Stopped moving. Surrendered.

"Oh," John breathed…. "so you like it when I fuck your mouth, do you?"

Sherlock couldn't speak, obviously. But he moaned. The vibration of it made John see stars.

"Well if you like it so much, why don't you touch yourself?"

John heard the sound of a zipper being pulled down. He leaned forward to watch. Sherlock managed to undo his trousers one handed. He pulled out a slender, pale erection and began to stroke it.

Shit.

John grabbed two handfuls of Sherlock's hair and started to fuck his mouth. Slow. He didn't actually want to hurt him. Sherlock dropped his hand to John's thigh. Kept touching himself with the other.

This wasn't going to take very long at all.

John sped up. Just a little bit. Chasing the wonderful friction. The tension built inside him. Coiling over itself. He couldn't take it.

"God, I'm going to…" he grunted.

Sherlock didn't pull back or shove him away. Just stayed wonderfully relaxed as he let John use his mouth.

John groaned. The tension collapsed. Crested. Crashed. He emptied himself down Sherlock's throat. He could hardly breathe. Felt almost faint. Oh god yes.

He released Sherlock. Let him pull back. The younger man hadn't stopped touching himself. His chest rose and fell rapidly—panting.

"Come up here." John patted his lap.

Without a word, Sherlock climbed on top of him. John wrapped a hand around Sherlock's prick and started to stroke him. Focusing the pressure around the head of his cock.

"Uhh…" Sherlock breathed. He rolled his hips forward. John sped up.

"Next time I'm going to fuck you," John whispered. "Just like this. First, I'll make you ride me. Take your own pleasure on my cock while I sit back and watch. And then, when you get close, I'll flip you over on your back. I'll fuck you so hard you won't be able to walk properly for a week."

"Please," Sherlock gasped.

That was all the warning John got before Sherlock tensed. His come dribbled over John's hand. Fell onto the couch. Onto John's trousers.

In that moment, John didn't really care.

Sherlock collapsed against him, breathing heavily. John ran a hand along Sherlock's back. Soothing.

"There's going to be a next time?" Sherlock asked quietly, after a few minutes.

"Yeah… I suppose so," John sighed.

Sherlock pressed a lazy kiss against John's lips. John returned it. Perhaps they were both more than a bit insane.

But if this was wrong, maybe John didn't want to be right after all.

I already posted this as a prompt fill on tumblr. If you follow me, you might be around next time I scream out to the heavens asking for a prompt. Do itt... taylorpotato . tumblr . com.