How was Sibelius on the accordion?

Britain's Independent reports on a newly unearthed letter revealing that Edward Elgar was a laughably bad trombone player:

www.independent.co.uk/arts-entertainment/classical/news/great-composer-shame-he-couldnt-play-1824125.html

Possibly related riddle:

Q: What is a gentleman?

A: Somebody who knows how to play the trombone, but doesn't.

Many more instrument jokes here: www.mit.edu/~jcb/jokes/