Disclaimer: No recognizable characters are mine; no money is made. (Now I worry that the characters aren't recognizable . . . ugh, this is not the sort of pressure I need in my life right now!)
Enjoy!
"—stimulation activates the parasympathetic response and acetylcholine will be released, causing vasodilation, causing arterial blood to fill the corpora spongiosum and cavernosa—"
". . . this is not what I meant . . ."
"Oh? I didn't mean it to just focus on me. The same will happen to the erectile tissue in your penis! Due to increased heart rate and blood pressure, you blush a very attractive rose color on your cheeks. I have noted that this flush is something that occurs in myself as well, and that it extends down to my chest. I believe this extended coloration is due to my paler skin and comparatively less melatonin; it allows the blood vessels to be seen more clearly under the epidermis—"
"This is wrong—you're going to have to stop—"
"Is this too physiological? I can, perhaps, simply go to the mechanics—"
" . . ."
"Foreplay is a bit of a gamble to deduce since, although we tend to fall into patterns, there is always a bit of improvisation as well. Kissing, licking—I'll pinch your nipples, you'll fumble a bit with the zipper of my trousers, the task made more difficult with the strain of the fabric because of my erection—"
"Sherlock—"
"—then of course, the decision as to how to bring each other to orgasm. Frottage is always enjoyable, but so is fellatio—mutual or otherwise. Of course, after proper preparations have taken place, and if you're so inclined—"
"Sherlock!"
"—I could my insert my erect penis in your arse, and commence rhythmic thrusting until—"
"Oh god, stop. Stop!"
"—neuromuscular euphoria results in ejaculation—"
"OH MY GOD, STOP!"
Sherlock, his words coated with the honey of his baritone voice, finally stopped. He looked surprised.
"But you requested that I 'talk dirty' to you—"
"Yes, yes I know, but that . . . what you were saying . . . oh lord . . . that was not talking dirty! That was . . ." John gave a visible shudder. ". . . that was clinical and weird."
"Clinical and weird?"
"Yes!"
Sherlock studied him. "Your state of arousal has decreased since you made your request."
"Uhmm . . . yes. Yes it has."
"So . . . there will be no sexual interc—" He saw the look on John's face and interrupted his own word to try again. "There will be no sex tonight?"
"Uhmm . . . no. Let's just go to sleep, Sherlock."
John turned to his side in a bit of a huff. Sherlock, his mind dissecting and re-hashing the entire conversation, re-fitting pieces back together into a new configuration, took a long time before drifting off to sleep.
fin.