Sherlock was always so careless with his wings. It made john incredibly jealous to see Sherlock flop into a chair and rather than tucking his wings neatly behind him as most would, he just let his wings fall where they would over the sides.
It made him angry that Sherlock would treat his gorgeous wings so badly while John tried his best to manage with his ruined wings.
It pissed him off that Sherlock never took care not to let his feathers get bent or caught against walls or railings or what have you.
It made him sad that he couldn't fly with Sherlock.
Fortunately, Sherlock didn't fly very often. He always took cabs, everywhere, and stated it was a more discreet method of transportation. John wasn't sure he believed him.

And now, seated in the living room, with tea in one hand and the post in the other, he admired Sherlock's wings. Sherlock was sprawled over his chair, black feathers a waterfall if ink over the sides. It should have looked like an untamed mess, but somehow Sherlock made himself look like a painting. Really too photogenic for his own good, John thought. He put his tea down.
But those feathers. Sticking out every which way. Each of them was flawless, and yet the whole ensemble was incredibly unkempt. It wasn't fair. He cleared his throat, and gathered a bit of courage before saying, "You really ought to at least straighten your feathers." There. That's all. He wasn't at all envious, just concerned for his friend's upkeep.
Sherlock opened his eyes halfway, and heaving a great sigh, dead panned, "Why," at John.
John swallowed. "Because your homeless network has neater feathers than yours." Oh, snark, perfect choice.
Sherlock blew out a breathe and let his head fall back. "There's really no need for me to look pleasant, John. I shouldn't want to give anyone a false impression of me."
John frowned. "Just-" he sighed, "try and take a little better care of yourself."
"Nope."
"Please, Sherlock."
"That's not my job, John, I solve crimes. You're the doctor."
Said doctor stood up, (a little too quickly) the post fluttering to the floor, and walked briskly to the bathroom. There, he grabbed a brush and some oil before returning to the detective and his massive wings.
Putting the oil down none too gently, he commanded Sherlock, "Sit up straight."
He pulled Sherlock's left wing out and began to straighten the offending feathers.
"What on earth are you doing, John?"
"Someone's got to take care of you." He didn't look up from his task, not even for a second.
Sherlock huffed and allowed his spine to curl into a resigned slump while his blogger worked away at his wings. After a while, when he felt he had done a satisfactory job realigning his feathers, he picked up the brush and began to detangle the down. The tiny feathers, John noted, had just a hint of blue to them, and were a shade lighter than the rest of Sherlock's feathers. Dutifully, he brushed all of them, although he may have lingered too long while smoothing them down. The softness of them was a harsh contrast to the knife-shaped points of the primaries and secondaries.
Oiling Sherlock's feathers, he was struck with a sadness; he did miss the primaries on his own left wing. He still had a couple, four to be exact, but they seemed awkward and out of place. He only kept them because their removal could cause nerve damage, and he'd already had enough of that. He'd have no qualms about losing those last few primaries, though. His dust coloured wings held nothing of their former glory. Instead, they generally hung useless against his back. Although he did make sure to keep his right wing in good shape, the absence of a working partner made it just as useless.
A voice interrupted his thoughts. "You've slowed down, and your movements have become less methodical. You work with a heavy hand. What's wrong?"
"It's nothing. Just wishing my wings were as nice as yours." He tried to make the statement sound dismissive, but to no avail.
Sherlock stood up, cautious of his wings, and took a stepped behind his flat mate. He carefully, and very gently, took the dull brown wings in his hands and thoughtfully stretched them out to their full width. He ran his fingertips over the feathers of his right wing, admiring the subtle colour variations. Like desert camouflage, he noted. He shifted his hands over to the salvaged left wing. Very, very softly he traced the lengths of the remaining primaries, each one of the secondaries, and then stroked briefly over the tertiaries. He pulled back suddenly, giving John a start. The dark winged man swiftly retrieved a chair from the kitchen.
"Sit. I want a closer look," he told John. "If I may," he added as an afterthought.
John got over his initial shock and managed to get out, "Of course," as he sat down, wings hung over the back of the chair.
Sherlock began further scrutiny of John's damaged wing, but he was so gentle and careful, as if he thought John were a fragile bird. As if he were something precious. It nearly made John tear up. He briefly wondered if this was how Sherlock handled all evidence. He realized then that Sherlock had probably been waiting for an opportunity to inspect his wing. So he settled in and let Sherlock do his thing.
After nearly half an hour of this loving scrutiny, he stood up, and pulled John up by the shoulders as he did. He lowered his head such that his mouth was level with John's ear. He whispered, "Your wings are beautiful."
John scoffed lightly. "You don't mean that,"he said, his voice soft.
"I do," Sherlock breathed, placing his hands lightly on either side of John's ribcage. "I always have."