A/N: Ooops I wrote porn. I've never written porn before so please excuse me if it's shitty. Feel free to tell me if it's shitty and if you have any advice on how to improve it.

WARNING: There are two men having sex here. If you don't want to witness that, I'd find another story to read.

DISCLAIMER: I don't own Sherlock or John, unfortunately. That pleasure belongs to the BBC. Please don't sue me.

Experimenting was one of Sherlock's favorite pastimes. He'd rather be on a case, yes, but at least he wasn't letting his brain rot.

And this experiment was absolutely fascinating.

He was so involved, as per usual, that he didn't hear John walk into the flat. He didn't hear John swear at the mess in the sitting room. He most certainly didn't hear John come into the kitchen.

"Sherlock."

Finally, the detective glanced up and looked surprised to see John standing there, arms crossed and looking rather...pissed off.

"Hello, John," replied Sherlock, nonchalantly.

John's frown deepened, and he gestured dramatically towards the sitting room. "Why does it look like a tornado went through the flat, Sherlock?"

The taller man just frowned a little. "Does it?" He cocked his head and was quiet for a second. Then he leapt up from his seat, abandoning the microscope on the kitchen table. "Ahh, yes!" He swept into the sitting room and glanced it over. "I was looking for one of your medical books, I'm trying to find out how long it would take to dissolve a human heart in stomach acid."

He shouldn't have been surprised. He really, really shouldn't have been. Sherlock had never cleaned up after himself, so John shouldn't expect him to start now. And it really didn't bother him, having to clean up after the detective. Although...yes, this would be the perfect opportunity.

When he and Sherlock had started shagging, no one seemed surprised. Not even John, who had been trying to deny his feelings for years, really ever since he and Sherlock had moved in together.

It was vanilla sex for a long, long time. Then, one day, John jokingly called Sherlock "Private" and Sherlock had leapt on him and sucked him off so well that John is still pretty sure he blacked out for a few minutes.

After that incident, John learned Sherlock had a MAJOR military kink. Not just a military kink, but...Sherlock seemed to thrive on being dominated. Something that surprised John at first. Sherlock Holmes was a force to be reckoned with and he didn't even let the British Government boss him around. It took some time to figure out why, but when John did, he was amazed he hadn't figured it out sooner.

Sherlock was always ranting about his mind never shutting up, about it whirring a million miles an hour. Somehow, this fact had escaped John's mind. When it returned, he figured it out. Being dominated gave Sherlock the chance to shut off his brain and let someone else take control.

John was surprised at how much he was turned on by the whole thing. He'd never gotten off on his position when he was in the army, but Sherlock was so bloody responsive. It was glorious. John said kneel and Sherlock almost dislocated his knees he dropped so fast.

Sometimes, at work, John would fantasize about these past experiences and he'd get so hard he'd have to skip lunch to have a good wank in the loo.

Today?

Oh, today was definitely one of those days.

"Sherlock," John said in his firmest, non-Captain voice.

His lover looked at him innocently.

"I want you to clean up this mess, right now."

"But John, I'm in the middle of a very important experiment!" Sherlock exclaimed, sounding precisely like Sherlock Holmes, World's Only Consulting Toddler.

"The experiment can wait. Clean. Up. This. Mess."

"Is that an order, Captain?" Sherlock drawled sarcastically.

Oh, the bastard. He knew exactly what he was doing. And John knew he loved it. John felt himself growing warmer, body breaking out into goosebumps. His trousers also suddenly felt incredibly tight.

After a few moments, during which Sherlock found his body mimicking John's, John cleared his throat. He stood up, straight, a posture befitting a captain. "It was, Private." Despite the commanding tone in John's voice, it was husky and God, if it didn't go straight to Sherlock's cock.

Sherlock hadn't dropped into his headspace quite yet. "What will you do if I don't?" His voice lacked its usual venom, and it seemed like he was trying very hard to keep it steady.

John just stared the detective dead in the eyes. "Disobedience gets you punished. You know that."

The whining noise, Sherlock would declare later, obviously came from somewhere else. Because Sherlock Holmes, even in the throes of 'oh God I might have a stroke because all the blood is going to my cock', does not whine.

"Into my quarters, Private." John commanded, in a low voice.

After he'd marched Sherlock into their bedroom, John stood with arms crossed. Sherlock, for once in his life, was quiet. Then, slowly, John leaned forward until he could hiss into Sherlock's ear. "On your knees, Private." Simple words, but words that caused Sherlock to hit the floor so hard his knees cracked against the floor and a sinful moan escaped his lips.

When Sherlock was here, on his knees, and John wasn't John but Captain Watson, it was an experience he wouldn't trade for anything. This was a high better than cocaine had ever given him. His mind was pleasantly blank and fuzzy, pupils blown and focused on one thing: doing exactly as he was told.

John looked down at his lover and- no. He couldn't smile, not now, not while he was in this role. He was so hard right now he could hardly think, but he needed something else. One more thing. "Wait," he commanded. There was no need. Sherlock was too far gone to do anything but what John told him. John left the room briefly, and when he returned he was wearing only his pants and...his dog tags.

The metal felt cold against John's chest, and it made him shiver. "Now, Private..." John leaned forward to hiss into Sherlock's ear. "You're going to suck on your Captain's cock until you are ordered to stop. Is that understood?"

Sherlock nodded. Immediately John reached through Sherlock's shirt to pinch a nipple, hard. The detective gasped, and John smirked a little. "I said," John repeated. "Is. That. Understood?"

Sherlock swallowed, nodded again, and managed a breathy sounding "Yes, Captain."

John made no further moves, and Sherlock took the opportunity to start mouthing lightly at John's clothed cock.

"I believe, oh my God, that I told you to suck, Private." John somehow managed to sound stern in spite of the urge to let his knees buckle and his resolve to crumble.

Sherlock looked up at him through dark lashes, the picture of innocence. "I'm sorry, Captain," he said, demurely, then...

"Oh, Jesus fuck."

Sherlock decided to remove John's pants with his teeth. While this was not strictly part of John's orders, he let it happen anyway.

Once he'd freed John's leaking erection, Sherlock wasted no time. He lapped at it first, inquisitive little brushes of that clever, clever tongue. He did that for so long that John thought he might cry because it just wasn't enough. Finally though, Sherlock took the head into his warm, perfectly wet mouth. He sucked gently, running his tongue over the slit and along the head.

By this point, John was ready to start pumping into Sherlock's mouth, but he was (somehow) able to restrain himself. And suddenly, Sherlock was fucking his own mouth with John's cock, engulfing it to the base and occasionally swallowing, causing John to choke out a strangled "Ngh, fuck Sherlock, just like that."

The doctor could feel the muscles in his abdomen tightening, so as much as it pained him, he pulled out of Sherlock's mouth. Sherlock made a soft whining sort of noise (and denied it later when John brought it up, of course) and looked up in confusion.

"Excellent, oh God, excellent work, Private." John said through labored breaths. The detective smiled weakly, then grunted in annoyance and ground against the floor. John chuckled lightly, then clicked his fingers and Sherlock rose.

"Now, Private..." He lowered his voice, and the effect on Sherlock was instant. The detective let out a quiet moan and shifted uncomfortably around the bulge in his trousers. "I want you to strip for me."

It took a few minutes for Sherlock's brain to catch up to John's order.

Ordinarily, Sherlock stripped slowly, almost preening like a fucking peacock for John. And oh, John loved it. Loved seeing Sherlock reveal that gorgeous body just for him. Today, though, in this mindset, Sherlock removed his clothing with single-minded precision. Well, as much precision as he could manage with trembling hands and legs that threatened to give out on him when he tried to remove his trousers.

Now just as nude as John was, Sherlock stared blankly at the doctor and waited.

"Lie down over there for me, Sherlock, on your hands and knees. And don't you dare touch your cock." The last command was given in John's sternest tone. When Sherlock didn't move, John narrowed his eyes. "Move," he growled.

Sherlock's entire body jolted, and the glazed look in his eyes receded, just a little, and he turned around and sat down on the edge of the bed. He lay back, then rolled onto his stomach and pushed himself up on trembling arms. His cock pressed full and hard against his belly, and he let out a whine.

"So impatient," John muttered, posture turning predatory as he positioned himself behind Sherlock. They had lube in the bedside table, but they never used it when they played like this. He slicked his hand liberally with the pre-cum from the tip of his cock, then swiped the pad of his finger along Sherlock's hole. Almost involuntarily, Sherlock pushed back minutely. John drew back his other palm and brought it down hard onto Sherlock's arse. "Don't. Move." He leaned forward and spoke directly into Sherlock's ear, causing the detective to shudder.

With little care for delicacy, John pushed his finger inside, and Sherlock hissed with pain. He was relatively quiet as John carefully moved his finger in and out. When he felt John add a second finger and begin to scissor them inside, Sherlock shuddered lightly and whispered "Fuck," very quietly.

"What was that?" John's tone was nonchalant, but his fingers stilled.

"N-nothing, sir," managed the detective. He started to push back onto John's fingers, but another hit to his arse stopped him with a quiet whimper.

"Lying gets you punished," said John, tone turning dangerous.

"I." It took a long moment for Sherlock to think of the words. "I said fuck, sir."

John nodded. "I thought so." Without another word, his fingers began to move again. When he brushed against the detective's prostate, Sherlock yelled so loudly John's ears rang.

"Ready?" It was a few more fingers and minutes later. The game was coming to a close now, because suddenly John's voice was kinder and gentler. Wordlessly Sherlock nodded.

"Alright. Remember the rule."

Damn. Sherlock had nearly forgotten. If he got fucked during these games, he wasn't allowed to touch his cock. He could come, of course (and luckily he could from prostate stimulation alone), but there was to be no touching.

Slowly John pushed himself inside, groaning at the tight heat. "God, baby," he hissed.

Sherlock suddenly lost all his restraint, letting out a moan so pornographic that John had to stop himself from coming right then and there.

Their pace was slow at first, but eventually Sherlock gritted his teeth and groaned out "God John faster, please."

John obliged him. It was a miracle that the bedframe didn't break. By this time Sherlock stopped making noises. Instead he just pushed back with each thrust, twitching a little when John brushed against his prostate.

Suddenly John felt Sherlock go completely still underneath him. When he looked down, he saw the come splash against the detective's chest and soil their top sheet. The feeling of Sherlock's arse clenching around his cock finally made him orgasm, emptying himself in the tight heat.

Once they'd come down from their high, John cleaned them off sloppily with a clean portion of the sheet. Sherlock then immediately curled up against his chest, nuzzling at the doctor's throat. John kissed his hair. "Love you," he said quietly.

Without opening his eyes, Sherlock mumbled "Love you too," before he drifted off to sleep.

Before he let sleep claim him, John took off his tags and set them on the bedside table.

For next time.

A/N: Thoughts? Feelings? Is it good, bad, awful? Thank you so much for reading! Please review and...

DFTBA darlings, :)