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John was by no means overweight, but Sherlock was by far skinnier, what with the naturally lanky frame and the truly atrocious eating habits, or lack thereof. While John was solid and stout with muscle and a healthy layer of fat, Sherlock had the wiry build of a runner and almost no extra padding to speak of. Furthermore, years of substance abuse and the continuing nicotine patches had done a number on Sherlock’s circulation—not enough to hinder him during a chase, but enough that most of the time, his extremities ran several degrees colder than the average male’s. This only exacerbated Sherlock’s naturally lower body temperature.
Accordingly, the shift from ‘just friends’ to ‘significantly more than friends’ had been accompanied by the sensible compromise: In winter, John would let Sherlock burrow under the covers with him and twine his frozen limbs between John’s, often eliciting undignified squeaks or squeals until John’s naturally warmer body heated Sherlock up. It was an acceptable inconvenience for John because Sherlock returned the favour during the hot summer months…
“Where has that blasted fan got off to?” John demanded, rummaging through their closet in little more than his pants. “Nine in the bloody evening, and it’s still thirty degrees indoors. God, I need air.” Rivulets of sweat outlined the contours of his torso, and he panted lightly in the unrelenting heat of the flat. Behind him, the front door opened and closed. “Sherlock? Do you know where the fan’s gone? It’s sweltering in here!”
“Mmm, no,” Sherlock replied, coming up to stand behind John. A burst of cold spread from a small bar on the back of John’s neck, fractals of chill winding up and down John’s spine. He jumped in surprise, twisting to see that Sherlock had pressed a nearly freezing bottle of water to John’s nape. “I got you some water while I was out, though.”
John sighed and accepted the water, unscrewing the cap and draining a good third of it. “Thanks. It’s something, at least. I don’t know how you managed to go outside in this heat, let alone in that much clothing.”
Sherlock shrugged and peeled off his suit jacket and dress shirt. “It’s not that bad. Look: I’m barely even sweating.”
After a few moments of irritably heated glaring (it was already too hot to really warrant a heated glare, but John just couldn’t manage a stony cold glare like Sherlock could), John grabbed Sherlock by the relatively icy hand and towed him to the bedroom. “Right. Clothes off.” He tilted back the bottle of water and downed half of what remained.
Grinning, Sherlock stepped out of his trousers and shoes, flopping back on top of the covers in just his underpants, looking like nothing more than a pale starfish on the background of their dark duvet. “Come here, then.” He gestured John down.
Happily, John spread himself across Sherlock’s chilled chest, sighing as some of the oppressive heat slipped from his skin to be absorbed into Sherlock’s lithe form. He twitched slightly at the startlingly cold touch of Sherlock’s hands on his back but couldn’t help a pleased squirm as his body temperature immediately began to drop.
Between the veritable human ice block below him and the light breeze from the window above, John felt his mood improve substantially with every passing minute. “This low of a body temperature isn’t healthy,” John muttered into Sherlock’s shoulder as the sweat on his forehead cooled, “but damned if I’m going to complain about it right now.”
“I’m sure you’ll more than make up for it in the winter,” Sherlock snorted, bouncing John a little with the motions of his chest. “Just give it a few more minutes, and I’ll have warmed to your body heat. That’s the downside to no fatty insulation, I’m afraid.” John felt Sherlock’s mouth twist into a wicked grin against his scalp. “But, of course, that’s when I can utilise that ice you put in the freezer an hour ago.”
John shivered in anticipation and dragged the bottle of water over for another sip. Later, when he grew too warm for their position to be comfortable, Sherlock did indeed fetch the ice to use on John.
And, if Sherlock’s method of cooling John down involved warming him up a bit in the process, well... John wasn’t about to complain.