both screw up Boeings

Here is a musical joke:
Why is a violist like a terrorist? They both screw up Boeings.

What is it actually 'screw up Boeings'?

and if it's not Boeing, what does it mean in relation to a violist? Does it relate to a terrible sound his instrument produces?

I think it is to do with a Volinist, screwing up, or breaking:

Boe Strings

or Boe Ings.

Sorry, my mispelling:

'Bow Strings' or

Bow-ings (Boeings): the pronunciation is the same, and that is the source of the humour.

In context: "arrangements for strings The fingerings and bowings on the violin part are meant to make it as easy to play as possible, eg, avoiding string crossings with legato bowing. ...

So, we got there in the end. Not a very funny joke.

Thank you, Robin. It's definitely bowing.