At the resort i work at, we tell all the rookies the theme is one thing, and all returners come dressed as something else. For example, when i was a rookie, we were told the theme was nappies, and we arrived, all in adult diapers, they were all in a beach theme. And last season, we told them the theme was geeks and nerds, and we all came as jocks and cheerleaders. More kitsch value in Aus coz we dont have jocks or cheerleaders...but you get the idea!