There’s a reason complete strangers keep mistaking Sherlock and John for a couple.
Sherlock, being Sherlock, always notices it when people are checking John out. He dislikes it. It makes him feel…panicked. However, John disapproves of him making rude deductions at unsuspecting strangers, so Sherlock has to find a subtler way to deal with such outrageous affronts.
Sherlock leans in close to talk to John, touches his arm to get his attention, smiles at him in a smitten way, steals food off his plate: all those behaviours he has observed in romantic couples. It is excellent; The dull cretins oogling his John invariably sighs in defeat (”Why are all the good ones taken and/or gay?”) and refrains from making any further moves.
John never notices. After all, Sherlock acts like this all the time, and John is remarkably unobservant.
Then Sherlock and John actually get together, and Sherlock comes to the pleasant realisation that it is no longer necessary for him to be subtle. So the next time a young barista twirls her hair and draws an anatomically-incorrect heart on John’s coffee cup, Sherlock wraps a possessive arm around John, presses a kiss to his hair, and glares at the offending barista over John’s head.
John turned around, smiling.
“What was that for?”
“You’re very attractive,” Sherlock said primly, all innocence.
John chuckled and slipped his hand into Sherlock’s, and they walked out of the cafe sipping their drinks.
“You know,” sip, “you react to competition like a twelve year old girl.”
Sherlock’s coffee burnt his tongue. He spit it out, spluttering.
“What are you talking about?”
“I mean this,” John demonstrated by stroking a hand down Sherlock’s arm exaggeratedly, “and this,” he leans up to breathe heavily into Sherlock’s ear.
“I thought you didn’t notice.”
“Yeah, not at first. But then that time at the Dancing Dragon you stole all the broccoli off my plate while glaring aggressively at the woman at the counter. And you don’t even like broccoli.”
Sherlock frowned heavily, reading to commence the world’s greatest sulk. But John was still talking.
“That’s when I realised,” John stopped and turned to face Sherlock fully, “that you wouldn’t really mind if I just-”
John put his free hand on Sherlock’s shoulder and snogged him full on the mouth, right there on the busy pavement. Morning commuters swerved to avoid the two of them, stoically ignoring them in that fine London tradition. He could hold up the traffic for once, Sherlock thought dizzily. Mycroft did it all the time.
“Anyway,” said John, clearing his throat and rolling back on his heels. “Just wanted you to know. Don’t get your knickers in a twist. You don’t have any competition. But if you still feel like snogging me in odd places, that’s fine with me.”
“At crime scenes?”
“Not at crime scenes.”
“But you just said-”
“Got to draw the line somewhere, Sherlock.”