Just got off the Seascape and it was NOT uncommon to see men wear jeans to the Yacht Club restaurant and there was no issue with them doing so.
Additionally, in response to a prior post - there were plenty of men and women wearing shorts in the Top Sail Lounge with no issues.
I am on a cruise to relax and enjoy life - not to "dress to impress". If I wanted to be forced to "dress up" for dining, there are several other lines I can choose to sail on. One reason I specifically choose MSC is because of their dress code!