Following in the tradition of "the Dirty Sanchez", this is a sexual act. This can only be done to a girl with hair at least 8 inches long. While she is sleeping you ejaculate in her hair, aiming to the front, specifically. Then, take a small clump of her hair,a t the very front and center, and pull it straight up till it's taut. Rubbing the seminal fluid and holding the hair until it dries, she will wake up with her hair resembling that distinguishing feature of a unicorn.
My girlfriend was being incredibly rude, and I was sick of it. So after she fell asleep, I rubbed one out and gave her The Unicorn and left for good.