I study and also work at a fast food chain, my boss is really volatile and gets angry really easily. My availability is only on the morning so I can study, I have explained this to him, but he always put me on the night because I do a good job and will show up no matter what. How do I ask him to put me in the morning shift in a way that's firm but also won't make him mad. I'm looking for another job and plan to use that as an excuse.