This starts right after Sherlock comes back after faking his suicide. Mary and John are not romantically involved, but they are rather good friends.
Sherlock was sitting in his chair, his hands pressed to his chin, as usual when he was solving a case. When John walked through the door he had to duck because immediately following his entrance Sherlock, unaware of John, threw his knife at the wall, hitting the doorframe about two inches above John's head.
"Is this how you greet people now?" John asked aproching Sherlock's chair.
"Mhm sorry what?" Sherlock replied, coming out of his mind palace.
John stared at Sherlock, had his friend really just said sorry to him or was John's mind playing tricks on him?
"John stop staring like a mindless git, it is not an impossible thing for one to speak is it not?"
"But you said sorry.."
"Oh did I? My stupid tongue, adding in words that are unnecessary for human interaction."
"Okay..." John stared to stutter, knowing that this was going to get them nowhere, "what's the case that is troubling you?"
"Nothing's troubling me, John."
"Sherlock you literally just threw a knife at my head a minute ago!"
"Oh," Sherlock looked at the door, with the knife sticking out of it.
Mrs Hudson entered the room, immediately troubled with the fact that a knife was now impaling her door.
"Sherlock, I just replaced that door, and now look what you've done," Mrs Hudson chided Sherlock as she went into the kitchen.
"While you're in there Mrs Hudson could you make me some tea?" Sherlock asked.
"For the last time Sherlock I'm not your house keeper!" Mrs Hudson crossed her arms and gave a sigh of frustration.
Two minutes later she came out of the kitchen with a steaming cup of tea. She set it down in front of Sherlock and promptly left the room.
Sherlock seemed unconcerned, "Fetch me that knife will you John that door still hasn't gotten what it deserves."