John wandered into the living room to find Sherlock staring at him violin angrily. "What's up?" he asked, and received a glare in response.
"Today is not a good day."
"What is it? Don't tell me. It's the anniversary of the first case you lost. No? Is there some obscure festival overseas that you've been banned from?"
"It's worse. It is the anniversary of my insufferable brother's birth."
"As opposed to your other brother?" John joked, then raised his hands in surrender when he found himself on the receiving end of another icy glare. "Sorry."
Sherlock turned back to his violin and picked it up, raising it to his shoulder lividly. He raised the bow to play, and John covered his ears. He removed them, though, when he heard Sherlock playing 'Happy Birthday to You' perfectly.
When the song was finished, John cocked an eyebrow at Sherlock. "What was that about?"
"That was for the benefit of Mycroft's hidden cameras. This is how I really feel."
John stuck his fingers in his ears and rushed out the door, but he could still hear the screeching. He ran downstairs and out the front door, only to find that he could still hear Sherlock's awful playing.
"Don't worry," he said to a pair of confused pedestrians outside the flat, "it's just his brother's birthday."