Sherlock stepped out of the cab and up to the door of 221b, slightly annoyed at Lestrade for telling him that case would be interesting. A man appeared to have shot himself in the head, twice- so what? Simple open-and-shut domestic, once you observed the facts. Not to mention, it was a complete waste of time. Still, he tried to be at least a bit understanding; after all, he couldn't expect everyone to see the obvious.

Upon entering the flat, he was surprised to see John, sitting in his old armchair and scrolling through some web page. He didn't appear to notice the other man entering the flat, and Sherlock removed his scarf and hung it on the back of the door before turning back to him and speaking up.
"What are you doing here?"
John's eyes darted to Sherlock, and he abandoned the website momentarily.
"Came to see you. There's no need to sound so defensive, it's not a crime for a man to visit his best friend, is it?"
"You just haven't been coming by the flat much recently," Sherlock said dismissively, "Is that my laptop?"
John smirked. "Of course. Not so pleasant when someone else takes your things without permission, is it, Sherlock?" He added when Sherlock gaped at him.
"But how did you get in?"
"Well, I was very simply able to deduce your passcode based upon my extensive knowledge of you as a person," John said mockingly. Sherlock raised his eyebrows skeptically. "You didn't shut it down," John sighed. His ex-flatmate nodded and made his way to the chair opposite him.
"How stupid of me. Can't be doing that," he muttered to himself as he sat, and then in a louder voice, "What are you doing, anyway?" John's face turned a bit red, and he sucked in his cheeks.
"Just checking the blog. Reading through the comments, you know."
"I see. Anything interesting?" Sherlock asked casually, fishing for whatever it was that was embarrassing John.
"Uh, you could say that," he responded hesitantly, continuing on when the detective looked at him expectantly, "Have you- have you heard of the phenomenon of 'JohnLock'?" Sherlock gave the laptop a suspicious look.
"No. What is that?" There was a very awkward pause as John took a few breaths.
"Apparently it's something that's pretty big with the people who read my blog," he said, "It's a combination of our names, obviously, John and Sherlock, like, together."
"As in..?" Sherlock looked, if not exactly surprised, nearly as flustered about this as John.
"Yep." John nodded.
"They know you have a wife, right?"
"That doesn't seem to matter."
Sherlock seemed to process it for a few seconds, then motioned for John to give him the laptop. "Can I..?" He sifted through the many comments until he came to one with a link to a 'fanfiction' and clicked on it. "These people read your blog, they ought to know your bloody catch phrase," he noted quietly.
"I don't have a catch phrase," John protested.
"Yes you do. Oh, and there's the reference to it," Sherlock said after reading a few paragraphs, and quoted the author's version of himself, "'"'I'm not gay' 'We are not a couple'. Methinks thou dost protest too much," the consulting detective teased, as he-'"
"'-slunk across the room to the other man, a suggestive smile dancing on his lips,'" John finished slowly, lingering on each of the words like he could taste them.
"Yes. How do you know how that finishes?" Sherlock asked, turning away from the screen. He looked up to see that John was no longer in his chair, but standing directly in front of him. His heart rate increased and his thoughts started to blur despite himself, as John placed both hands on the arms of his chair and leaned in towards him. It almost seemed that their roles were reversed, now; John was studying him, analyzing, and undoubtably noticing more than Sherlock was willing to show. Sherlock tried to discourage the involuntary reactions his body was exhibiting. He repeated over and over in his mind that love was a human error he could not afford, but made no difference. His hands crept towards John's.
Apparently, John approved of everything he was seeing, because he continued to advance until their faces were centimeters apart. "It's mine," he whispered, and Sherlock had to think for a moment to remember the question he had asked seconds ago. "I wrote the very first Johnlock." With that, he brought his mouth down on Sherlock's, crushing them together, and Sherlock was no longer able to contain himself. He cupped John's jaw with his hands, opening his mouth and laying his teeth softy into the other man's lower lip. After minutes of tangling tongues and teeth and lips, Sherlock pulled away shook his head slightly, confused.
"Wait, sorry," he murmured, out of breath, "What about Mary?"
"Oh, her." John laughed quietly. "About that- she kind of has a girlfriend."
"What?" Sherlock's surprise was cut off by another kiss being planted on his lips. No longer restricted by that one worry, he wrapped an arm around John's waist and pulled him in. John obliged, climbing up in the chair, on top of Sherlock, and straddled his lap, his fingers making their way to the strained buttons of the tight purple shirt. Sherlock's hips hitched upwards, sending a jolt of pleasure through John, who gasped and shuddered against him. He felt Sherlock's erection and his own pressing together against his stomach, hot and flush despite the layers of clothing between them. The other man moved a hand down and unbuttoned his trousers, but John pushed his hand away and slid off of the chair, and Sherlock stood with him. Gradually, stopping a few times along the way to slam into the wall and focus on the movements of their mouths, the two of them made their way into Sherlock's bedroom. Sherlock pushed John against the door, which slammed closed, and removed his shirt faster than John had previously thought possible, panting heavily in his ear. When he again tried to get John's trousers off, John shoved him roughly away, causing him to fall back against the bed, and slipped deftly out of his trousers and pants.
Dropping to his knees beside the bed, he slid a hand into Sherlock's waistband and held eye contact with the other man as he pulled off his pants. He crawled up and kissed his partner, making sure that was the only place their bodies were touching, and undid one shirt button at a time. Sherlock yanked his arms out of the sleeves and flung the shirt across the room. His hands tangled themselves in John's hair, but John grabbed his wrists and forced them to the bed, holding him down. He licked across his jawline, kissed his collarbone and sucked the smooth ivory skin of his neck, and continued trailing his tongue down his body, sliding backwards until he found himself kneeling again.
He brushed his lips against the head of Sherlock's cock, drawing a stifled noise from him. His tongue dragged from the base of his shaft to the tip, swirling it around, and finally opened his entire mouth around it. As he vigilantly worked his jaw, Sherlock groaned, jerking and thrusting his hips up. When at last he wrenched his hands free of John's grasp and clutched the back of his head, holding him in place, John moved away. He stood and got onto the bed, grabbing Sherlock's legs and spreading them wide. He lifted them over his shoulders and Sherlock's ankles locked together behind his neck.
John popped one finger into his mouth, and then a second and a third, slowly, putting on a show for the watching, hungry-eyed Sherlock. He gently pushed the fingers against Sherlock's entrance, slipping them inside him and using them to work his tight muscles. Once his partner was loose, John pulled his fingers out, which made Sherlock grumble in protest.

"Please," he panted.

"Please what?" John teased.

"Please, fuck me," he responded, without hesitation.

"As you wish." John forced his cock into Sherlock and threw his head back, a low moan escaping from both of their lips. He set a slow, fixed rhythm, pulling all the way out of Sherlock and slamming back in again, and wrapped his hand around Sherlock's cock. The other man began to groan a rambling list of curses along with John's name, and before long John was doing the same.
"Oh Christ, Sherlo- FUCK!" John shouted, and he gave a wordless cry as he came inside Sherlock, who was close to follow.
"God, yes. Yes, fuck yes. Oh!" He screamed as John's contracting fist got him to come.

They lay there for a while, breathing heavily, a mess of bare limbs and sheets.
"Johnlock," Sherlock mused, seemingly to himself, a little while later, "Why didn't I think of that?"

"Because you're an idiot," John responded immediately. Sherlock laughed, kissed him, and smacked him in the head with a pillow.