A.N. Wrote this a while back, just moving it here from my LJ.
Sherlock stared at the man standing across the street by the lamp post (early twenties, swimmer's build, very handsome, overpriced jeans and underpriced t-shirt, obviously in between boyfriends) and swallowed. His fingers twitched against his thigh, and he leaned forward despite himself.
"Sherlock?" Lestrade sighed as he walked up to the bench that Sherlock had curled up on. "I called you here to investigate a murder, not loiter with in-oh." Lestrade cut off mid-sentence as he followed Sherlock's line of sight and noticed the man.
"Oh," said Lestrade with ill-concealed desire. He closed his eyes, as if to savor the image, and licked his lips.
They stayed silent for a minute, neither of them moving, watching the man across the street. The man took his right hand away from his mouth, looked at the watch on his left wrist (his bicep flexed as he did so) and tapped his foot impatiently, unaware of the two men watching him intently.
The minute stretched on and would have lasted longer, but they were interrupted by a familiar set of footsteps approaching from the crime scene.
"Sherlock!" John's voice sounded quite harried, but neither Sherlock nor Lestrade paid any mind. "Sergeant Donovan needs the inspector to-"
He stopped short as he came upon the odd scene: Sherlock, sitting straight-backed on a grimy metal bench, and Inspector Lestrade, paying the four bodies in the nearby park no heed, staring, entranced, at a ridiculously good-looking young man smoking a cigarette across the street.
The young man dropped the cigarette and crushed it underfoot, and Sherlock and Lestrade both let out identical sighs as the last tendrils of smoke rose lazily from the crushed pile of ashes.
John stared at the two in disbelief, taking in the nicotine patches proudly peeping out from under rolled-up shirtsleeves, and pursed his lips.
"Oh, really," he said, and he stalked back off to the crime scene, leaving the two nicotine-starved addicts alone in their misery.