"Well, I'm so sorry, but you already have a commitment to meet with a very important patient at 12 for a CPAP. I'll see you then. Or we can explore whether the payor with whom you have a contract and from whom you get a lot of business thinks that this is acceptable."
I have no idea if this kind of situation is covered in doctor/insurer contracts, might be handy info before pulling that.
Also, holy cow, rampaging jackassery.