This can only be done in the school during the "Raining Blood" sub-chapter in Chapter 3: Lamentations. At one point the fire sprinklers will go off, but instead of water they are sprinkling blood everywhere. Run and slide down the blood-smeared hallway to get the "Slip And Slide" achievement. You need to gain enough speed before sliding. Do not equip your camera, as it will slow you down too much. This is the only opportunity for a 12 meter slide. You can replay this section through chapter select at any time.