When he was four, he was the ring bearer at his aunt's wedding.
Second husband of course, but his aunt (like most of his father's family) loved pomp and circumstance, so he found himself in a scratchy suit and bowtie, miserable and insufferably warm.
After the wedding at the reception, he'd been made to dance with the flower girl, some distant third cousin from somewhere in the north. At the end of their shuffle together, she'd puffed her lips out and planted a sloppy, poorly-aimed kiss on his lips. He meant to pull away, but he heard the adults' adoration over the movement, so he'd let her kiss him.
Until she tried to hold his hand. He drew the line at the kiss, thank you very much.
When he was sixteen, a girl in his sixth form cornered him against a set of lockers and had proceeded to grab him on either side of his jaw-line and kiss him swiftly. He hadn't protested, simply letting her proceed, collecting his own data as she mauled his face. She'd been red with embarrassment, and had run off immediately without saying a single word.
His lips had tasted of pudding and coffee afterwards. How strange.
When he was twenty-two, he'd let a strange man kiss him.
He'd been high, high as a fucking kite. The fellow had asked him if he'd ever "batted for the other team" before. What a silly euphemism. He'd answered no, and then the man had blathered on and on about some sort of "awakening" or "epiphany" in regards to his own homosexuality (which was a rather poor cover for his singular desire to pull Sherlock), and then the next thing he knew the man had his lips against his, his tongue prodding at the edges of his mouth, demanding entry.
He'd let him kiss him for a while (finding the sensation deliciously intoxicating while in his current state), but had refused the hand rubbing up against his thigh. No epiphanies here, thank you.
When he was twenty-seven, one of his clients kissed him on the cheek.
She was a widow, a clever and kind widow, and he honestly wasn't bothered by that kiss so much.
When he was thirty-four, a drunk pathologist tried to kiss him.
Well, she succeeded, but probably not to the effect that she'd hoped for. They were out for a pint at the pub – Stamford, Lestrade, and Molly – and the poor, hopeless, hopeful Molly Hooper had stumbled up next to him at the end of the evening, latching onto his arm for support as they'd waited for their respective cabs.
"You have th-the loveliest eyes," she mumbled, before reaching out suddenly and throwing herself against him.
Her lips were soft and warm against his, but he had no desire to kiss any intoxicated human being, let alone Molly Hooper. But he let her kiss him anyways, enjoying the distraction, before hailing the next available cab and hustling her inside without another word. She looked back mournfully at him as he shut the door behind her and let her be driven away, disappointment in her doe eyes as her gaze lingered on his figure on the pavement.
The next time he saw her, she didn't mention the incident at all, only blushing once as he entered and stammering a few times out of embarrassment when she spoke. Oh, Molly.
He was thirty-five when his roommate kissed him.
He honestly, truthfully never saw it coming. They'd just come back from Scotland Yard, having solved yet another case for Lestrade (as per usual), when John had – out of the blue – reached out to him in the doorway as they stepped inside, taken him by the arm, and kissed him firmly on the lips.
He pulled away almost immediately, and looked totally and completely appalled. "Sherlock, I- I'm so, so sorry, I didn't mean-"
But the doctor never finished his sentence, because Sherlock had grabbed him by the waist and pulled him back flush against him, their bodies pressed up into each other as Sherlock lowered his mouth to John's, the movement of his lips urgent and fevered. They stayed like that for a few moments, wrapped around each other, catching their breath, before breaking apart once more.
John looked up at Sherlock, confused but happy. "I thought- ?" he asked, puzzled.
Sherlock grinned. "So did I," he answered, before engaging his mouth (and John's by proxy) otherwise.