Battling with Yorick
Of course, John has his own tricks too. You cannot live with the great Sherlock Holmes without figuring out a thing or two to make the mastermind do your bidding. And while, John will always admit, he is no where near as clever as Sherlock (but he is damn clever), and he will never outsmart the man, but, since he is his, umm, lover, he can manipulate the things Sherlock wants. Sherlock's desires. Which sounds horrible, but John doesn't do it much, or often, and he mainly does one thing.
He hides Sherlock's skull.
John will find Sherlock, skull in his lap, mumbling, barely audible, patches on his arm, fingers beneath his chin, often eyes-closed, and he will go for hours, without telling John a thing. And John hates it. Hates not being the one Sherlock confines in, and found himself jealous of... of a skull?
So when Sherlock finally had to deal with the fact that he was still human and relieve his bladder (he does not take the skull to the loo with him, thank goodness), John grabbed that piece of bone and hid it.
When Sherlock returned, he did that adorable thing he does when he's looking for a clue he can't find, when he puts one hand on his head and turns around quickly in a circle one way and then the other, scanning the room with that impeccable brain of his, just like he did on the first case they worked when he couldn't find the pink lady's suitcase. John has to do his best not to smirk as the genius cannot find his skull and must resort to talking to John instead.
It's tricky though. John must make sure that everything looks exactly as it was, or Sherlock will find the skull easily. That not an impression in the rug is different, or a smudge has appeared on John's cheek, a book cannot be a centimeter further from the wall than it was; even the dust must be as it was, or Sherlock will see right through it.
And while it is a challenge, John takes great pride in his ability to hide that skull from Sherlock, because he knows it makes him the only man to best Sherlock, even if it is something small. (Although, he won't admit it, John does have the constant nagging in the back of his mind that Sherlock always knows where the skull is and is merely playing along).
Eventually, Sherlock stops talking to the skull altogether and only talks to John (it takes about a year, but does happen).
Except when John is not around - attending business about town or gone to visit Harry - and Sherlock is left alone in the empty house with nothing, no case, few experiments, no John, just him and Yorick and his thoughts. He picks up that skull and tells it how wonderful John is. He tells that skull all the things he's afraid to say to John, because everyone who knows him, eventually hates him, and the only one who hasn't left him doesn't have the legs to do so.