(What follows is silly and nsfw - don’t read it if you object to either of those things.)

Everyone always thinks that Sherlock is the serious one, given to taking offense, eschewing the silly, the preposterous, and often wrong-footed by spontaneous laughter. Of the two (and they are always taken together, compared only to one another, so impossible is it to consider them separately) John is easier, heartier…funnier. People think.

They’re wrong, of course. They so often are.

After their relationship has been established for some time, after the desperate, hungry first times have given way to the wondering, leisurely second, third and fourth times, after John begins to be able to consider Sherlock in his pyjamas or his sheet without wanting, without needing to stake his claim anew, after Sherlock is caressed gently enough times to begin to believe that perhaps he can expect loving touches as his due, that they will come again, and again, and that he need not therefore soak them up as perishingly as he did at first, that his desert of loneliness is indeed greening, and the process is not poised to be reversed at the slightest shift in the weather – after all these changes have taken place, Sherlock discovers, to his great surprise, a delight in the ridiculous. During sex, particularly.

It begins accidentally.

It is late, and John is tired, and Sherlock is finishing a slow, gentle blow job intended to help John unwind after a long day. John’s climax – which has washed over him rather than slamming into him, he’s not as athletic as he once was – has been over for several minutes, but he hasn’t lapsed into oversensitivity as he often does, and Sherlock is taking advantage of the rare opportunity to lavish languid attention on John’s soft penis. John is submitting to the attention with good grace, but he’s getting sleepy, and eventually he shifts his hips.

“Time for bed. Sherlock. Sherlock, get off. It’s time to go to sleep.”

“Mister Cranky just got a nice blow job and now he wants to sleep.” Sher lock speaks his grievance to the air and the four walls, not looking away from the object of his ministrations.

John says, “Did you just complain to my penis?” And giggles.

He didn’t, but because Sherlock loves that giggle, he does now. “And now he’s laughing at me. That’s gratitude for you. Honestly, little penis, the man has no manners at all.” And he kisses the drooping head of John’s long-since-flaccid cock.

“Sherlock.” John is attempting to look stern, not an easy feat for a man in his position. The mirth is bubbling close to the surface. “Sherlock, cut it out.”

“Shh, don’t interrupt.” Sherlock takes his thumb and forefinger and presses the aperture of John’s foreskin together so it flattens out. “Look, it’s a mouth.” He kisses the ‘lips’. John giggles again.

Sherlock stops there, for now, and instead moves up John’s body to rest his head on his partner’s chest, and allows John to idle through his curls as they both doze off. This was by far the silliest he has ever been in bed, and he observes with bemused interest that he really enjoyed it.

He begins to address John’s penis somewhat regularly, simple greetings (“Hello, little penis, what shall we do together today?”) and observations (“John has been ogling my arse since breakfast, little penis, what do you suppose he wants?”) or running commentary(“Oh, you like that, do you, little penis? So do I. Don’t tell John.”), whatever crosses his mind. John puts up with it for a short while, but eventually protests, though he must first stop laughing to do so.

“Sherlock, this is silly.”

“Excuse me, little penis, John has something he’d like to say. Sorry, John, what was that?”

“You can’t keep talking to my penis.”

Sherlock, impossibly, exchanges an incredulous look with John’s penis. To John, he says,“Why on earth not?”

“It’s ridiculous.”

“And? I happened to read on the Internet that it’s a sign of strength in a relationship if you can laugh together in bed.”

John is momentarily derailed. “You were reading about relationships on the Internet?”

“Are you listening to this, little penis? John is – Oh!” Sherlock gives John a knowing look. “I see the problem, I do.” He nods slowly, tapping the side of his nose.

John narrows his eyes suspiciously. “What, exactly, do you see?”

“It’s not the fact that I am talking to your penis that you object to.”

“You don’t think so?”

“No. I should have seen it sooner. It is, in fact, the manner of the addressing.”

“The manner – what do you mean?”

Sherlock leans in conspiratorily. “Little penis. That’s what you don’t like. And fair enough, too. Your penis is, in fact, quite large. It might not even know it’s the one I’m talking to. I can see how that would – er – rub you up the wrong way. Never fear, John, I’ll soon rectify the matter.”

From here on in, things get very silly, very quickly, as Sherlock comes up with names that he feels adequately reflect the size of John’s member.

Pleasure Club.

Paradise Cudgel.

Love Truncheon.

Occasionally simply Billy.

As each monniker gets more absurd, John gives up even trying to contain his laughter. He quickly becomes inured to the idea that an amorous Sherlock, in a particular mood, will inevitably address his penis as often as he speaks to John himself, so that at the end of a very brief period of adjustment, John hardly bats an eye when Sherlock bellows from the bedroom,

“Get in here, my Lustful Cockmonster, I have big plans for you and Doctor What’s-His-Name!”

(Neither does Mrs. Hudson on the other side of the not-at-all-soundproof floorboards, by this time. But then, she always knew Sherlock was the funny one.)