Outfit for a birthday party?

I am going to a birthday party today at Dave and Buster's (a kind of upscale arcade and restaurant) and I'm not quite sure what to wear. My friend (who the party is for) is a tomboy so I know she won't be dressed up, and the setting is casual. I want to look nice and neat, but I am a kind of a tomboy and don't want to be decked out in a frilled top or skirt. I am going to be moving around and dancing, so comfort is a priority. Please help?