It's easy. Dress as the posted policy states and cruiseline enforce their policy.
I don't care if someone enters the MDR in shorts if the policy allows, but object if the policy does not allow shorts and pax are wearing them. That makes me feel overdressed by following the policy.
Just got back from a B2B in the Carib. on the Reflection. Told my Wife, I am not taking my tux on Carib cruises any longer, will on other itineraries. Won't take a suit, but will wear an open shirt and sport jacket on format nights.
Not long ago got turned away on a Princess ship when I entered the MDR for breakfast wearing a new tee shirt. I was dressed for an excursion we were taking after eating. No problem went back to the cabin and put on a golf shirt.
O F C'er