I was on the Sapphire last halloween. Most the crew and some passengers dressed up in costume and there was a party. I think they judged costums and gave prizes.
Of course they decorated the ship with carved pumpkins and all.
A few of the crew had on some questionable costumes. I don't know if it was cultural or what but a few of the guy's had extremely tight and thin pants! I guess I should expect some scarycostumes on Halloween!!!