Rebar Pie is an Achievement/Trophy in RAGE. This Achievement/Trophy can be earned by using the Rebar ammo type for the Nail Gun to pin a piece of an enemy's body, or the enemy as a whole, to a wall. Achieving this will be fairly self-explanatory as soon as the player equips the Rebar ammo type. Not that this can only be unlocked after downloading RAGE: The Scorchers.