John likes to cook, and he's good at it. One of his many thinking skills is thinking of new, unique dishes that would tickle his taste buds in all the right places.
The thing is, the one person he cooks for might be the most picky human on all of earth. He's even more picky than infants with formula or three year olds with sweets.
And Sherlock knows the right things to say when John's cooking.
"Oh, John, that smells like insert-disgusting-bodily-fluid-here."
Or
"Hey, that looks like something I found at Bart's the other day."
Or
"I wonder if that tastes like whatever fungus was growing on that tree the other day, remember, John? The one that made me sick for days?"
When one of these lines comes out, John picks up whatever he's made and tosses it in the garbage, then turns to look at Sherlock, who has a very pleased look on his face.
"Ok, ok, what do you want?"
"Chinese."
John hangs his head and put his coat on.
What Sherlock does like John to cook, well, bake, is cake. And cookies. And cupcakes. And lemon bars. And fudge. And anything, anything sweet. John could pick up a rock, sprinkle some sugar on it, hand it to Sherlock and watch the great detective attempt to take a bite out of it.
John is really good a baking. He uses the same cooking skills to perfect his treats, and uses the treats to perfect Sherlock. Once, John went on a baking spree and made two cakes, three kinds of cookies, and two dozen cupcakes, all of which were completely gone in two weeks, give or take a day. Sherlock was so happy with this, he did everything John wanted and asked for. John was so happy with this, he considered quitting his job as a doctor to pursue a career in pastry arts.
That is, until Sherlock became sick for days after.
"You do this every time, sweetie. You make yourself sick."
"I wouldn't be sick if you didn't have to bake so damn much."
"I'm sorry I get bored."
"Shoot something, like me!"
"Been there, done that."
"Oh, shut u-" Sherlock was cut off by the sound of his own vomit.
John rubbed his back and gave him tea, hoping it'd all go away, but it didn't go away for four days.
Needless to say, John didn't bake again for a very, very long time.