Ok, this my first time writing Johnlock, so I hope it's ok :)
A Study in Poisoning
John blames Sherlock.
It was his turn to pick up dinner but instead he decided to go chasing around some of London's criminals and wouldn't be home til late. So John got take away from this little Thai restaurant a few blocks from their shared flat, which is why Sherlock blames John for their current state. Because clearly you could see that the chef had been in prison by the scull tattoo on his arm, which was barely visible since his arm was covered with a variety of tattoos. But Sherlock sees everything. Like that the woman who served him was a part time Go-Go Dancer and how did Sherlock know that? Because there was traces of glitter on her clothes and her make-up was far too heavy just to be working in some shabby restaurant.
And of course Sherlock knew that he'd been served by her because she'd written her number and name on one of the napkins, using the cheap pen that she kept tucked behind her right ear at all times. John hadn't noticed it the number scribbled on his napkin, he'd been too eager to get home to Sherlock. Even though Sherlock had clearly pointed out all these facts (that he'd picked up from the time he went to get lunch but decided he'd rather go hungry then have food poisoning) they still ate the Thai anyway. John figured it couldn't be that bad, they'd been a few people there when he arrived, so surely Sherlock was wrong and they wouldn't end up with food poisoning.
Sherlock's never wrong though.
That's why they've both spent the last hour (and five minutes, six seconds) emptying their meals into the toilet bowl. John's leaning against the bathtub, hair flattened down with sweat, a wet wash cloth pressed to his forehead by Sherlock, who is lying down on the cool tiles beside him. The doctor gently brushes the detective's damp curls away, running a wet cloth across the younger mans forehead. Sherlock smiles up at him, a soft genuine smile that is only ever offered to John, it makes his heart beat faster.
"We should go to bed" John said, slightly disappointed at the thought of moving.
"No, I'm fine here" Sherlock replied, reaching up to twine his fingers with the doctors.
John smiles, he wants to kiss Sherlock but it would be rather awful after all the vomiting they've done, so instead he lifts Sherlock's head onto his lap and continues to stroke those wild curls. "You knew this would happen, didn't you?"
Sherlock opens his eye, a small grin tugging at his lips. "I had to prove a point."
John can't help but roll his eyes; of course Sherlock bloody Homels would risk food poisoning to prove a point, to prove that he knew more than most people on this earth. "You're getting dinner next time, ok."
Sherlock closed his eyes again and let out a sigh. "Fine, if I must."
They fall into silence; it's a rather perfect moment even if the circumstances are rather unpleasant. But the sickness has subsided and all that's left is the feeling of love and happiness.