The party may not take place during traditional work hours — but that doesn't mean you should dress like you're going to a nightclub.
You should wear clothing you wouldn't be embarrassed to wear to work, but, since it's a special occasion, it's fine to take it up one notch — just don't go over the top.
"It is a party, but your attire needs to be suitable for a business event, not a nightclub. Don’t wear anything that is too short, too tight, too low, or too anything," advises Pachter.
Also, if you normally wear a suit to work, don't show up to the office party in jeans and a T-shirt — or a Hello Kitty onesie.