as a theatre major myself for my undergrad, YS probably doesn't really like the whole working in a business thing. I know I didn't.
That being said, it should be up to his boss (OS) to talk to him if YS is not being a good employee. If YS was employed elsewhere, you wouldn't get involved would you? He's 19 and we all have to go through this sort of stuff at some point. Hugs!