We were married on the Disney Magic the year before last. We travelled with 20 other family members and we let them know before hand that we had two rules for the trip (hey, we were paying, so we made the rules).
1) They could go their own way all day, but had to be at dinner
and
2) They HAD to dress up for Pirate Night.
We took extra hats and props for those we knew would balk at it.
We all had a blast. DH, my nephews and my SIL really got into it and talked like a Pirate all day long. We even got our waiters in on the act. They had lots of fun! Who cares what other people think. We're there to have fun. If they don't like it, they are just stuffy unfun people. Disney is meant to make every adult a kid again! That's what makes the trips so special. It is a time to let loose and just have fun for the sake of fun!
There was a couple on their honeymoon that sat at the table behind us that actually rented professional costumes for the trip. They looked amazing!