Adult costumes are a great way to commemorate a period of time, whether past, present or future. More and more adults are realizing the benefits of being able to find that one of kind costume 24 hours a day, 7 days a week, days a year. Adult Halloween Costumes Ideas Adult Halloween Costume Top Themes. So, just because you’re an adult doesn’t mean your interests have completely matured. Sexy Halloween Costume Themes. Your Halloween fun has evolved over the years, and while candy and trick-or-treating were Fun Adult Costume.