You are the face of your sorority!
Stepping down from my soapbox... give me a second.
No matter what day of the year it is, I urge you to remember you are representing your organization 24/7. Halloween, among all of the holidays throughout the year, is one of the most important days to set your reputation. This is a day that is dedicated to costumes, drinking, and dancing while you're in college. Everyone is congregating at parties on campus and off campus. Booze is flowing, and before you know it you are tempted to dance on a table and stick your tongue out like Miley. Well, look how well that turned out for her. Sure she is getting more attention from the media, but is it really the kind of attention you and your sorority deserve?
Having attended several Halloween parties in my undergrad days, and trying on several slutty costumes, I can attest you will have so much more fun if your butt is not hanging out of your too-short skirt all night. You won't have anything to apologize for in the morning. You won't have unflattering pictures to answer to in the morning. Pictures, I might add, your future employers and your mother will find no matter how hard you try to hide them.
On every other day of the year, you don't have to think about the cat ears you might wear and how they will clash with your leather hotpants. But you should still keep in mind the clothing you wear and what it says about you. At an interview, for instance, you don't want to show up with your legs hanging out there in all of their glory. Make sure to be conscious of the length of your skirt. Try it on, and practice sitting in it. Practice walking up stairs in it. Make sure it covers all essentials, and I would recommend it touch your knees.
When you sit in said skirt, whether it is your recruitment outfit or your perfect interview suit, pay attention to what happens when you cross your legs or ankles. Does the skirt get too tight? Does it gap? These are things you will think about in the moment and become distracted by if you don't test it out first.
Be prepared. Be modest. You'll be more comfortable in the moments that count.