I have a theory that relates to how people pick out their costumes. I think it 1. directly relates to how much attention they are in need of and 2. Has a real window into their personality.
1.The "sexy" costume.
This is the costume that gets the most attention period. So for most girls and some guys, they choose this route because they want people staring at them. Ooogling them. They LOVE it. If they say otherwise, they are lying through their perfect teeth.
On the personality part of the equation, I think these people think they are FUN, but are usually more consumed with themselves and their "image"
2. The "SCARY" Costume
Attention is not as big a deal for these people, but they would like to get a "reaction" out of people...usually involving screaming.
Personality wise, these people probably have a fascination with the grotesque and could be anywhere from normal intrigue to seriously needing therapy.
3. The "celebrity" Costume
Attention can vary on this one based on what celebrity is being presented. If we are talking madonna with the cone bra, then they are probably needing more attention than the person dressed up as Nixon.
On personality, I think this person is probably either is up on their fame and pop culture, or just really loves or wants to make fun of the character they are dressing as.
4. The "Funny/Clever" Costume
This person wants to draw attention to how smart or creative they are. They want to be seen as funny and innovative. They want people to laugh or just gawk at their awesomeness.
Usually this person is really fun to be around. They are typically the people you want on your friends list :)
5. The "non" costume
This Person does not want attention. They don't care. In fact, why did they even come to this stupid party?
Either this person is "too cool for school" or they are so busy / lazy they don't consider it worth their time to put effort into a stupid costume.
Well there you have it. Please don't debate, my science is sound :)