A/N: Well I read something with some really angsty angst and I just about exploded so this is my fluffy, fuzzy, adorable and slightly awkward fix-it for me. If you enjoy it too, so much the better.
As a couple living alone, more or less, you get used to having a certain amount of privacy for, ahem, romantic activities.
Put more bluntly: a couple without kids isn't worried about where they screw.
John and Sherlock had, until quite recently, been a childless couple. The adjustment period was taking awhile.
That is why one afternoon found John with his hands on Sherlock's hips, nestling up against him from behind and pulling him away from his less-than-vital experiment on the kitchen table, all the while whispering naughty things in his ear. He steered him over to the couch, kissing the back of his neck and rubbing up and down his arms. Turning him around, he nudged Sherlock down onto the sofa and indicated that he was to lie down. As he did so, John climbed onto the sofa and over Sherlock, straddling his thighs. John bent to kiss him, and ended up initiating quite a passionate snogging session, for lack of a better term. Being healthy men engaging in such activities, their bodies responded with certain expected physiological reactions…
Just in time for Astrid to bbburst through the door and launch into what seemed to be a very promising story about showing up her English composition teacher.
Of course, when one's newfound teenage daughter walks in on you getting handsy with anyone, even if it is your long-term partner, it's awkward. Especially when the both of you are at this point less-than-fully clothed, in possession of very mussed hair, breathing heavily, red-faced (and not just from embarrassment, either), and feeling each other up. That's why John felt the instinctive urge to jump off Sherlock and stand to one side of the couch, awkwardly, much like he had the time his mum caught him trying to get Julia Ward's knickers off. Unfortunately for John, both then and now, he'd had a rather obvious indicator of arousal. Luckily, or, depending on your point of view, unluckily, this time so did Sherlock, and it was a hard (no pun intended) decision as to which one was more obvious.
Shielding her eyes and blushing furiously, Astrid began to stutter, "Never mind… I'll be, um, anywhere but here. Ok bye," she shouted behind her as she ran upstairs to her own room. Neither John nor Sherlock could get a word in edgewise.
A few seconds later a call came down: "Just… inform me when you're decent, would you?"
That was the night they decided on an indicator for "Do Not Enter, Copulation In Progress."