Please, don't get me wrong with this post, it's my opinion and I hope it can help you to not cross that fine line, so you can be the sexier girl in the party without everyone thinking: "Oh God, she looks like a total slut"
Every girl wants be sexy, and Halloween it's perfect to that, it's a day where you can be anyone else except your, everything it's allowed! But... I don't want to look sluty with my costume, I want to show legs, keep men eyes on me all night but I don't want to be labeled as "Easy Girl" because of my outfit.
So here are a few examples of Dos and Don'ts with the most common costumes.
First of all, length of skirt, on the left side ("Sluty") you can almost see under her skirt, a lot of skin is showed, but on the right side ("O.K.") it's longer the dress, the right amount of skin is showed, the lace sleeves, in my opinion, are so damn sexy.