Is dress suit optional on costa concordia.
Captians dinner - Dark suit/dinner suit/white shirt & ties or tuxedos, Ladies Cocktail dresses, pantsuits, elegant skirts and blouses; evening gowns. On the informal type evenings just shiirt/tie/trousers/jacket and for ladies trouser suit/smart dresses and on the other evenings trousers/summer tops and for ladies similar attire.
Informal evenings: not necessary to wear suits or ties for men - dress code is smart/casual - smart trousers and shirts with collars would be fine and smart wear for women.
Formal evenings: suits (either dj or day suit) with ties for men and anything goes for women! Dresses/trousers/skirts and tops although usually with a bit more sparkle and bling!!