> 1) It seems that to a lot of girls, Halloween is just a chance to dress really slutty. I mean, it's all good and fun to look silly, but slapping on a short, short white skirt and calling yourself an angle is just stupid.

I'm not-very-successfully resisting the evil impulse to make a pun about "acute angle". Oh well.

Fancy dress of all sorts is often about wish fulfillment. People want to look attractive, or heroic, or romantic, or impressive, or dangerous, or whatever. If girls want to be considered sexy, fancy dress occasions like Halloween might give them the chance to go beyond what they feel they ought to be comfortable with in normal situations. "I'm not REALLY slutty, I'm just dressing like this for Halloween! ... but I look good, don't I?"

I'm not getting into whether this is a good thing or a bad thing. It's the way people are. Maybe everybody needs an occasional outburst into silly pretendy games.