What do you call a doctor of philosophy?
When I was an undergraduate, the answer was straightforward: "Doctor [lastname]" or "Professor [lastname]." These days, I generally call them "firstname," except (a) sometimes when emailing (I write several registers more formally than I speak, especially when asking for favors!) or (b) when dealing with someone particularly eminent or senior. And even (b) is a diminishing category.
But it's never crossed my mind to demand that someone in an informal or presumptively collegial setting call me "Mr." Much less have I ever dreamt about being called "Professor" on a routine basis. (I still think the first time should be pretty fun.)
A recent contretemps has shown that apparently some holdouts on formality remain, something that is deeply ironic considering the presumably egalitarian norms of the professor in quo. The comments section was, as often happens, livelier than the post, particularly FLG's question "Would you accept Dark Lord Alpheus? Or Darth Alpheus?"
So now I know what I will insist my students call me once I've received my doctorate: Darth Pedantus.