What a shame that you did not enjoy your costa cruise, we have just returned form out Costa Serena cruise and loved every minute of it. Costa are resort ships and i do think that your holiday is always going to be what you make and do with it. Holidays are meant to be relaxing and i guess that this does spill over into what we wear as well. There is usually the option to dine in the formal restaurants where you can dress for meals as opposed to the lido buffet areas where the poolside and open decks are far more casual as people are swimming and sunbathing and this is obvious as you approach these eating areas. The onboard info. re the ships usually provides this kind of information so that you can pre-plan your days and eating habits. we usually find that if you smile and engage people with friendly chit-chat that it is reciprocated and we found everyone lovely.