Dress appropriately for the function you're attending. You should know the dress code for your office's holiday festivities -- and if you don't, you should make it your business to find out. Many people take the office party as an invitation to show off "who they really are" and let loose. There's nothing wrong with being yourself, but be yourself within reason. That low-cut, skin-tight cocktail dress might work in the club, but it's not the outfit you want to wear in front of your company's CEO. And if your office party is informal, don't show up wearing your fanciest evening gown.
Our advice to you is to be appropriate, fight the urge to make any wacky fashion statements, and remember that the classic little black dress works just about every time. Happy holidays!