It's the still slightly-obscene nature of the act that makes him love it. It's not, of course, illegal, but yet…it maintains an aura of a-little-less-than respectable, we-don't-talk-about-it anywhere, je ne sais quoi.

Regardless, John Watson's tounge in his arse really is, by all measures, one of the most spectacular things he's ever experienced. How they got here, one leg thrown over John's shoulder, stark naked on his sheets isn't so much a mystery as is the why, or the why now.

"I bet you anything you'd care to lay down that you can't." Sherlock has John pinned against the wall of the flat, running his nose down John's cheek to whisper softly against heated skin.

"Oh, it's that kind of challenge, is it?" john breathes. "I'll be more than happy to." John grasps Sherlock's shirt and pulls him closer, flattening himself between Sherlock and the wall. Sherlock's breath hitches a bit as John scrapes his teeth lightly down his neck. "I'll make you come and more; I'll make you scream my name till you're hoarse, I'll make you beg."

"Dare you," Sherlock says, a scant distance between his mouth and John's, a tiny separation that keeps this still as chaste as they want it to be, an opportunity to retreat which neither takes.

John pushes Sherlock's jacket off of one shoulder. "You're a bastard, you know that?

"I'm not," Sherlock counters, licking his lips, "I can be good. I can be very, very…good."

"But when you're bad you're better?"

Sherlock's gleaming, sharp smile is his only response.

" So, this how you want it then, a game? Then I'll claim you as my prize, because if we do this, I won't give you up."

"Nor I, you." Sherlock slides a hand around John's waist, presses against him until they're touching from chest to knees, Sherlock's mouth descending to capture John's in a deep, wet, dirty kiss.

Sherlock's having a harder time holding off his orgasm than he thought he would, trying desperately to send his mind elsewhere when John slides smoothly into his arse, his cock curved just perfectly to glide against his prostate with every stroke. He decides to get a bit of his own back and tightens down on John's cock, lifting his hips in a sultry undulation that has John's eyes rolling back in his head.

"I see you struggling, don't think I don't," John gasps, and falls over him, one arm braced next to Sherlock's shoulder, the other lifting his leg around John's waist. "May as well give up now."

"I'm pretty sure I'm not screaming," Sherlock snaps back, the tension making him sharp. "Is that the best you can do?"

John narrows his eyes and adds a little snap to his hips at the end of every thrust, jolting Sherlock up the bed and making him gasp. "That do for you, persnickety?"

Sherlock can't respond; he's seeing stars, stars and the universe besides, the warm smell of John's skin and his aftershave enveloping him, sending him off into a different reality entirely. All he can do is exist in this moment, right now, the slick sheets of his bed behind his back and clutched in his hands, John's cock making him feel achingly full, surrounded, taken.

Christ, it was the worst bet of his life, he'd had no idea John was this good, no concept that sex with him would be this consuming. He wanted him, oh yes he had, taunting him into taking the chance that neither had been quite ready for. But now that they're here Sherlock is kicking himself for not having done it earlier.

John leans down and kisses his chest, licking at a nipple, making Sherlock groan from the sheer overload of sensation. John's smile when he lifts his head is smug and Sherlock realizes that at this point he doesn't give a damn who wins what; coming under John's strong, compact body is more than enough compensation for his own body's weaknesses.

"God, touch me, John, please, please, touch my prick…"

John's triumphant smile lights the room. "Ah, there it is, you gorgeous thing. Let me have it, let me have that lovely cock of yours." John curls his hand around Sherlock's cock and strokes, softly at first, just a light squeeze of his fingertips on silky soft skin and unyielding hardness. He's trying desperately to get Sherlock there before he comes himself; Sherlock is tightening up, his body milking John's cock and it's all he can do to keep breathing. John tightens his grip and strokes harder, long, slow pulls that leave Sherlock tossing his head back and forth on the pillow.

"God, yes, yes, coming, oh John, I'm coming, Oh God, John!" he shouts, coming hard, his body shivering, semen spilling across his stomach and down his side. John keeps thrusting through it until Sherlock reaches up and grabs John's arse and pulls him in harder, lifting both legs until his ankles are over John's shoulders.

"Oh, Christ, Sherlock, I, I, oh – " and he's over the edge, arms wrapped around Sherlock's bony knees and his eyes screwed shut.

Sherlock waits quietly until John opens his eyes in the aftermath, pleased see the happy, sated, bright blue gaze of his dearest friend, and he smiles.

"Best prize I've ever won," John says, kissing Sherlock's ankle where it still rests on his shoulder. He carefully withdraws and collapses on his side. "When you're ready, I think I'd like to claim it."

Sherlock chuckles. "Isn't that what you just did?"

"Oh, no, that's just the game. Now comes the real fun." John leers at him, reaches down and caresses Sherlock's now-soft prick. "I think I'd like to have my legs over your shoulders, when you're ready."

Sherlock can feel the ridiculous grin forming on his face. Oh yes, so much better than a game, better than a tease, better than just about anything he's ever imagined.