Originally Posted by You
Some lines are more casual and indicate this. NCL and Carnival come to mind. HAL is not as casual, but many consider the "suggested wear" means it is only "suggested," and so, there is no problem with wearing whatever.
Ah, no. A "suggestion" by a person in authority (in this case, an officer of the ship acting on behalf of the master of the vessel) is NEVER optional.
Also, the norms of social etiquette dictate that guests at a social event are to dress in the manner prescribed by the host or hostess who extends the invitation. Failure to do so is exceedingly gauche.
Of course, there are always some who are hell-bent on demonstrating their ignorance and their arrogance to everybody else....