FBS or "Fuzzy Butt Syndrome" is a condition in which hair grows on the buttocks. The thickness of the hair can range from a light peach fuzz in mild cases, to full blown carpeting. (See HBS) This condition plagues millions across the world. There is no cure to FBS though there are treatments including shaving.
Person 1: "Hey your shag toilet seat is really comfortable!"
Person 2: "My toilet seat isn't shag, I bet your FBS is just acting up."
Person 1: "Oh noes!"