The only time Sherlock will play the violin badly, is to annoy his brother, the rest of the time, he plays it beautifully.

John... John once blew out both Mycroft's and Moriarty's entire network of electronic bugs in 221B with the god-awful sound he made.

He's had more than one of Mycroft's attendants curled up in a corner whimpering in pain.

Moriarty uses listening to John's attempts as punishment for any mistakes his minions make.

And Sherlock is pretty sure their home hasn't had any kind of pest since John decided he wanted to learn.

John's just trying to get better at playing, though constantly being asked by Sally and Anderson to play during interrogations, is kind of rude.

At least Lestrade just puts in earplugs.