One of these days I'll get back to my other stories. Anyways I've never actually dealt with this sickness before, so if it seems unrealistic, that's why.
On to the story!
No matter what he was doing, Sherlock Holmes always appeared to be in constant motion. So when the man in question began shifting himself around in his seat, John barely spared him a glance.
It wasn't until Sherlock was lying flat on the couch forcibly rubbing his back against it that John finally closed his newspaper with a sigh. "What are you doing?"
He pointed to John's laptop that was sitting precariously on his chest. "Checking emails."
Inhale. "Let's try again. Why exactly are you attempting to sandpaper the sofa with your body?"
"Oh. I have an itch."
"And you can't, I don't know, scratch it like a normal person?"
"Tried that, it didn't go away." Sherlock glanced at him. "Say John-"
"No I will not scratch your back for you."
"Why not?
"Because you are in your mid-thirties, and are perfectly capable of handling this yourself."
"Early thirties."
"Whatever helps you sleep at night."
A full two minutes of Sherlock mimicking a cat marking its territory and John pretending he didn't notice, passed before the latter finally snapped. "Alright fine. You're driving me mad. Turn around."
With a smug smile that showed just how pleased he was to get his way, Sherlock allowed John to begin scratching the middle of his backside. He let out a low moan.
"New rule: no making noise while I'm itching you."
"It feels good though."
"Doesn't matter." At a certain point, John happened to glance up towards Sherlock's neck, and noticed something that made him pause. "Um Sherlock?"
"Hmm?"
"You've had chicken pox before right?"
"How should I know?"
"Everyone knows if they have or not."
"Obviously not."
"Knows how to disembowel a bloody turtle, but not his own medical- look I'm asking because I'm almost certain you've contracted it."
Sherlock chuckled idly scratching at his arm. "Oh John. I see those years of medical school were wasted on you. Only children get chicken pox."
"Anyone who hasn't had them is at risk of getting them."
"Since when?"
"Since.. always. Don't huff at me, I'm trying to help."
"I think I have some calamine lotion, it'll help with the itching. And don't scratch, you'll scar."
By the following morning Sherlock was covered almost completely in little red marks, and proving just how awful a patient he could be.
"Holmes, I swear I am going to Phoebe Buffay your hands."
"I don't know what that means."
"Stop scratching."
"But it itches!"
"Then use the ointment!"
"But it smells funny."
"Oh. My. God."
As John was contemplated the likelihood of Lestrade letting the homicide charges slide if he told him that Sherlock was being really annoying, a distraction in the form of Mrs. Hudson arrived. "Oo oo. Oh," She clucked. "Aren't you a sight. Poor bean." At this, the world's only consulting detective let out a self-pitying little whimper that made his landlady give a sympathetic tut, and his friend roll his eyes. "How about I run you a nice oatmeal bath, hmm? It'll be just what the doctor ordered." Sherlock gave her a wide forced smile, and waited till she had tapped her way out of the room before turning to hiss at John, "I refuse to sit in an oatmeal filled bathtub, like sliced fruit in your morning bowl. I refuse!"
Adding oatmeal to the ever growing list of foods he couldn't eat without thinking about his flatmate naked; John looked back at him. "Sorry Sherlock, you heard what she said. It's what the doctor ordered."
The look of betrayal only sweetened John's petty, if fleeting, revenge.