The King is Dead - Silent Auror
With his own clothes still in the suburban flat, John needs Sherlock to lend him some of his:
Once he’s stepped out, John towels off and looks at the pile of neatly-folded clothes in curiosity to see what Sherlock’s chosen for him. There’s a pair of plain black socks, a pair of underwear which appear to be made of satin or silk or something slippery that feels expensive and luxurious in his fingers, and a navy-blue cashmere jumper. John’s brain has got snagged on the pants, though. He’s stuck where he’s standing, holding a pair of Sherlock’s underwear and feeling the material like he’s a teenager touching a pair of girl’s knickers for the first time. This is ridiculous. It’s just underwear. Trust Sherlock to have such ridiculous, expensive, poncy pants. He steps into them and can’t help but notice how they feel on his skin, cupping his arse and bits with a whisper of material like a breath. He looks at himself in the mirror and thinks they look rather good on him, too. He also notices that his face is flushed and that he’s sporting a bit of wood. Oh, perfect. Fantastic. John takes a deep breath and tries to calm himself, putting on the borrowed socks and his own jeans. The jumper is last and it feels almost as nice on as the pants do, the cashmere finely-knit and very soft. The shade of blue brings out his eyes and makes them look bluer rather than the grey they can be sometimes. The jumper fits him perfectly, only it’s nicer than most of his jumpers and he immediately loves it. Sherlock never wears jumpers – perhaps he’ll let John keep it. Though, given what he now knows about Sherlock, he’s not sure that asking him for presents is precisely the right way to go about handling this whole thing. Really better just to not say anything at all. Right. That’s what he’d decided last night already, wasn’t it?
And last but not least a Silent Auror special trope

“I’ve – I’ve never done this,” John pants as Sherlock presses himself into John, both finally nude, Sherlock’s cock pushing into his stomach. “Not with a bloke, I mean.”
“I know that, idiot,” Sherlock murmurs, attaching his mouth to John’s ear. “I hardly think it’s rocket science. I’ve done my research. You’ll be fine.”