This guy has the right idea! (YouTube link)

He has style, I'll admit, but I still got the impression he seriously considered bashing the phone owner around the head with something that wasn't his violin...

Absolutely perfect response - yes, he was very annoyed, and quite rightly too, but an excellent musician's reply .

I wish I could just play stuff by ear like that. What a way to shame the mobile owner!

You could respond by playing this:

http://www.youtube.com/watch?v=gYpO6M-LyY8

That would be his viola then

Play the viola, keep the violin especially for dealing with idiot audience members?

Very nice! I'd like the sheets to that!

Classy...and more importantly, it worked in context. Spur-of-the-moment improvisation wasn't invented in the 20th century, and his response was as baroque as could have been expected under the circumstances.

As this video shows, his idea was nothing new:

http://www.youtube.com/watch?v=RpliR35_p68

It is a proper piece anyway, by Tarrega. Why didn't he play the whole thing? Epic Fail.

To keep with the theme, this has been doing the rounds on Facebook this week:

Now I finally get the joke! Curse my damned inability to sight-sing.

Excellent