The world's only consulting detective certainly does not need to use his deductive abilities to comprehend that John is upset with him. It always takes him longer than the average (dull) person to realize that his words have negative effects, but never with John. He is always able to tell, with startling immediacy, when he has upset his friend (friend, how appalling).
Sherlock steeples his fingers under his chin and lets his eyelids sink half closed as he considers the man in front of him. John stands at the window, the sunlight behind him throwing his face into a sharp relief of light and shadow and Sherlock can see the lines of distress in the man as easily as he can tell whether or not a person has pets, or if they pay for their coffee with a stolen credit card. He can also tell that John's eyes are focused on nothing at all, indicating a preoccupation with their conversation.
"You knew this about me," Sherlock says, finally, breaking the silence. He wishes he hadn't (shouldn't care). John's eyes refocus, first on the windowsill he was gazing blankly at, then flick to Sherlock himself.
"No, Sherlock, I really didn't," John spits with sudden intensity. He turns slightly, and rests against the edge of the windowsill, his hands clenching slightly around the worn wooden frame. "You've not mentioned it. I think I would remember."
This is Sherlock's fault, he knows this. He sits there silently as John fumes. He resists the urge to close the front of his robe tighter around his chest to hide what has made John so angry. He is not, as a rule, self-conscious, and especially not with John. He recognizes the slight twinges of nervousness in himself though (how revolting). "What does it matter?" Sherlock queries in a low tone, hoping to sound aloof but unable to stop his eyes from dropping away for a moment. He knows why it matters. John cares about him the way normal people care for their friends. Of course he is upset. Any normal person would be (normal being the operative word, of course). What he doesn't know is why he pushes John's buttons when he knows the doctor is furious to begin with.
For a long moment, there is nothing but silence and the sound of John taking a long, slow breath. The doctor's hands are clenched so tightly on the windowsill that his knuckles are white from the pressure.
"Sherlock," John begins, his voice a rasp as he attempts to control his temper. "You've just admitted to me that by the age of 21, you'd been shot twice, stabbed four times and broken no less than 14 bones, all trying to 'solve crimes'. That's not including any injuries in the last twelve years to bring us to today," He pauses for a moment, squeezing his eyes shut in a grimace. "It matters," John grinds the word out, "because you've never said. I had to find out because you forgot your bloody shirt, and the scars were visible. Not because you thought it was relevant. You never said, never thought that it would something your doctor- no, sod that- your friend should know.
John's temper is not entirely within his control. Sherlock knows this. He's seen it often enough in the older man and today is no exception. Sherlock always knows when the good doctor is liable to punch someone. The detective's hands fall to the arms of the chair he's in (John's chair...) and he tilts his head to the side. "You want to hit me," Sherlock says, curiously.
John blinks, and his expression hardens, but he doesn't deny Sherlock's claim. Sherlock shrugs, in what he hopes is a nonchalant manner. "So hit me," Sherlock offers, genuinely interested in whether the doctor will take him up on it, given his current temper. It wouldn't hurt for long, and he knows he can trust John not to take advantage of the opportunity by hitting him more than once.
Instantly, though, John's face softens and seems to fall slightly in an emotion Sherlock can't place for a moment (Ah, disappointment). John is disappointed in him. Curious. He wonders why. There is a long silence, and John levers himself off of the windowsill quite suddenly. The doctor closes the distance between them so rapidly that Sherlock wonders for a moment if perhaps John will hit him after all and half braces himself for it. Instead, the man crouches in front of Sherlock, one hand simultaneously balancing himself and grasping Sherlock's hand that is resting palm down on the armrest. The detective does not pull away; merely glances at their hands.
"Sherlock," John says, pulling the detective's eyes back to his. "I hit you once, when you asked me to, do you remember?" This brings a slight smirk to Sherlock's face as he recalls the small scuffle they had a block from Irene Adler's townhouse. John, on the other hand remains serious, his eyes never leaving Sherlock's face. "I want you to know right now, that I swear to God, I will never hit you again. Not even if you ask me to. Do you understand?"
Sherlock watches his doctor for a moment, mind whirring as always. "Why?" He eventually asks. "That seems a strange thing to promise." A lie. Not a strange thing at all, and he knows it, but even that idea makes him uncomfortable. He doesn't have friends, not really. At least, not before now.
John sighs, his head dropping a little, his grip tightening on Sherlock's hand momentarily before he glances back up. "I think you've been hurt enough, Sherlock," He says, before straightening up from his crouch.
Sherlock knows what is about to happen. He always knows when John is about to show him some sort of physical affection. He can't explain why (lying? How tedious, Sherlock,) but he always allows it to happen. John leans down, and his hand slips into Sherlock's hair at the base of the detective's neck. The doctor goes to press a kiss into Sherlock's dark curls. Normally Sherlock sits still, lets it happen and never says a word. There is too much in the action that feels like family, that feels like home, to interrupt. Today though, he feels... what is it? Remorse, he realizes, that he upset John so much. In the blink of an eye, Sherlock tilts his head back intercepts John's chaste kiss with his own lips.
It's over in a split second, and Sherlock wonders afterwards if perhaps his action was a bit not good, but John is still there with his hand in Sherlock's hair. The doctor's eyes are laughing and one corner of his mouth crooks up in his amusement. Sherlock tips his head to the side, trying to decipher what John's reaction means.
"Still not gay, Sherlock," John tells him. The tone of his voice is fond, and he straightens, his hand slipping from Sherlock's neck.
The detective shrugs for the second time in their conversation and closes his eyes rather than watch his friend leave the room to put the kettle on. "I know that." He says, a slight derisive tone in his voice (just checking).