When we cruised (7 day), on formal night 95+% of the men were in minimum a suit and tie. About 30% were in tuxes.
In all honesty, those not in at least dress pants, dress shirt and tie really stuck out. I heard one couple arguing becuase she ahd wanted to bring dressier clothes and he had talked her out of it, and she felt very out of place.
There was one disgusting family that showed up underdressed for Mc Donalds in sweaty shorts and t-shirts, and not only did they stick out, but many were rather repulsed by them and their obvious lack of personal hygiene.
On the seven night,
DCL does request FORMAL wear on formal night. Formal wear is a suit and tie for men, and formal dress for women. IMHO that should be respected, and the bare minimum would be dress pants with dress shirt and tie for men, and a "church dress" for women.
The 3 and 4 day seem to be much more casual, with no "formal night", and a shirt and tie with slacks would be fine
Anne