Someone acting insane like an animal or ghost. Such as screaming, running, or just acting completely idiotic and fake.
That girl Libby is the biggest banchee I have ever seen, all she does is run down the hallways screaming and sticking her butt out like she is cute. She is annoying, don't you hate her? I heard she make her voice sound like that because she thinks it is cute. F.Y.I it isn't!