At this point, I'm wondering if Mike isn't bipolar. He yells at her to not call her Michael when as a pony, but doesn't yell at her for calling him Michael when as a human. I'm also wondering if he's not trying to destroy what happiness he can get in Equestria. Rarity didn't work out (so far) because she's a serial killer. Milky only expresses her disapproval and he blows up in her face. I get that relationships aren't easy and that friction between two individuals will happen, but he's handling it like an angst ridden teenager, rather than the rational, reasonable near-senior citizen that he's supposed to be.