If you're feeling moody and not so much in the Halloween spirit, Billie's outfit in her music video for "When The Party's Over" is easy to pull off. Honestly, you probably already have it in your closet.
What to wear: A white t-shirt, leggings, and sneakers. You'll also need a blue wig, chunky silver jewellery, and some costume makeup (if you've seen the video, you know).