Sherlock likes attention, but John does not. This meant almost constant public embarrassment when they weren't on a case and Sherlock got bored. Sherlock would make it his goal to be as ridiculous as he could be to test how long it would take John to get up and walk away.
One time, this time, they were on the Tube and Sherlock was moment by moment, inch by inch, scooting closer to John. He put his arm around John, his hand clenching John's opposite shoulder. John's cheeks turned red in an instant. Not only did he not like public displays of affection, but he also didn't like when Sherlock acted this way for fun.
Five minutes later, John shifted uncomfortably in his seat and looked at Sherlock.
"Sherlock, stop, please."
The lady across from them looked up from her phone and watched curiously. Sherlock knew three other people on the train were watching, just to see what Sherlock would do next.
He looked at John, then at John's hand, then grabbed John's hand. John let out a breath of uncomfortable air, and shifted in his seat again.
"Stop it."
Sherlock leaned in to John and whispered in his ear, "People are watching, John. You don't like attention?"
John shook him off and stood quickly. "No, no, no. You sit here, I'm going to stand over there." And he did.
Sherlock smiled and a few people chuckled; his mission was accomplished.
Their stop came and they both got off separately. John walked on, not waiting for Sherlock, and Sherlock slowly walked behind him with no agenda to keep up. When they got to 221B, John opened the door and closed it before Sherlock could get inside.
When Sherlock got to the top of the stares, the door was shut and locked. He knocked.
"John? John, open the door!"
No answer.
"John, come on, I'm sorry, I was just having a bit of fun!" Sherlock's finger stroked the wood in front of his face. "I'm sorry!"
No answer.
"John, I will break this door down."
No answer.
Shower.
"Oh, come on." Sherlock whispered to himself.
In five minutes, Sherlock was in the apartment. It wasn't the first time he'd broken into the apartment, the first time was three months ago when John was asleep and he really needed to use the toilet, and the second time was three weeks after that when he locked himself out when he went to buy milk, which he'll never do again.
Ten minutes after he broke into the flat, he was undressed and apologizing to John against the shower wall.