Of course he had known.
As John Watson stalked through the streets of London, kicking slush angrily out of his way, he reflected to himself that of course he had been an idiot for thinking Sherlock wouldn't know. It was the most bloody irritating thing about living with that man. The hours? John could get over the hours, move past the front door of 221B Baker Street slamming shut at precisely whenever he happened to be dozing into anything, God forbid, resembling normal sleep. The experiments? John could move past those, too, could pretend not to notice the human eyeballs wretchedly preserved in the refrigerator and ignore the weird tribal ritual Sherlock seemed to conduct every other Wednesday with the femur of a yak. The gay thing? John could reassert his sexuality as many times as he needed without breaking too much of a sweat. But the sheer condescending omnipotence of the man? Now that was going to get Sherlock murdered one day.
John wretchedly wondered if the man would notice a poisoned English muffin coming.
Sherlock managed to ruin anything. Everything. Just by sheer dint of his maladapted genius, his child-like nitpicking, and that bloody thing he did with his eyebrows that seemed to say, "Oh, and you've not been proven to have been at some point cross-bred with a dog? Interesting."
Good Lord. He couldn't do this all day.
After all, it was nearly Christmas, and he needed to get the good genius a present.