This is a story-related achievement and cannot be missed. It will unlock upon defeating Hazmat 'Jimmy', the boss at the end of the Prologue.
Later into the Prologue while searching for Nick you will come to a gate leading to San Romero High School. A crew of zombies will attack you, one by the name of 'George', defeat them. Afterward, three zombies in Hazmat suits will attack you. The leader will have a health bar with the name 'Jimmy'. Oddly enough it does not mention his name in the achievement description like the other 6 bosses. Be wary of the explosive tank that 'Jimmy' will throw at you once he's low on health. Avoid it at all costs as it will decimate your health!
Once you defeat all three zombies you will get this achievement.