I don’t know how I missed John’s worried, guilty and pained expression in this scene when he realises that he’s made a huge mistake writing about Sherlock’s lack of general knowledge in his blog, because it’s resulted in Sherlock being the butt of leg pulling even more than usual and it physically hurts.
…and when the office bursts into derisive and snide grins John does his best to silence them by shaking his head at them, and you can actually SEE him beating himself up inwardly about it, because this genial, mind-blowingly intelligent detective is far more sensitive than anyone could possibly imagine and that it has been years of taunts and cruelties like these that have turned this perfect face into a wall of impeccable silence and emotionlessness, while John has destroyed all that and more by a few inadvertently placed words on a blog he believed nobody read. In the short time that they’ve known one another, John has come to understand the vulnerability hiding behind the facade - one that Sherlock must have hoped John would not reveal to others; however, he feels as if he’s failed him. He’s allowed the world to enter their little domestic settlement close enough to poke fun at Sherlock, for no fault of his own, beyond that John couldn’t keep his own mouth [fingers] from blabbing. His jaw clenches and head shakes as he feels Sherlock’s pain and confusion. He hurts because despite being the brave soldier that he is, the one person who needs his strength is also the one who he so thoughtlessly let down. He hurts because Sherlock hurts. And what hurts far more is the fact that he is the reason why Sherlock hurts.