On the subject of sexy girl costumes.

I'm not sure, having never been a young man (or at least not recently enough to remember), but as a young woman you find yourself observing a theme about clothing. If you put Cinderella in a ballgown, her stepmother won't recognize her and the prince will fall in love with her. Or, in every other Sandra Bullock movie, we can convince ourselves that if you tie her hair up and put glasses on her, she isn't pretty anymore. With enough primping and the right clothes, anyone can suddenly look beautiful.
Now, as a costumer I can attest to there being some truth in this. There is such a variety in every part of creating one's appearance, hairdressing, makeup, carriage and costuming that if you think there is no way any given person cannot become a work of art, you are simply wrong. Anyone can, with the proper effort, time and materials, can transform into something striking, something artistically beautiful. Whether or not that will fall into their own (or their chosen mate's) range of what they find attractive or not cannot be guaranteed, but beautiful and attractive are two different things.
But, like any other art form, beauty is hard. And people don't like doing things that are hard, especially not for something with the strange double standard of "appearance doesn't really matter, beauty comes from within" and "it is good to be beautiful". This means we have it in our heads that we must be beautiful all the time, but not put effort into it. Which frankly, I find disrespectful to beauty as an art form. It's hard work.
So if you don't want to apply the time and energy into find what about yourself is beautiful and accentuating that; (which I can understand, as it is hard) you might take a much simpler alternative. Substitute "sexy" for "beautiful". As a costumer, I can say that sexy is generally much easier to achieve. There is much less variety in legs than, say, faces, and most people feel more confident about the sexual appeal of their legs than the aesthetic beauty of their face. So the first step is usually to bear them. Often the bosom will also be exposed or accentuated. A single layer of petticoat about a foot in length is another common addition, when there is a skirt, which serves to further feminize the outfit, accent the hip to waist ratio, which as we all know has been a indication of physical attractiveness for much of history (stupid nineteen twenties throwing off statistics) and in some cases present the bottom's exposure as a possibility. As you can see, this is a simple formula and easy to achieve, and can be applied to nearly anyone or anything.
But beauty without sexualization takes time and effort; and many people do not want to exert that into something they will be wearing for less than ten hours for one day. I do not know what happens when a lazy young man wants to be beautiful for ten hours a year. Drinks alone and cries, I suspect.