Head Cheese Achievement
Kill all butcher shop enemies with headshots. "You're not PAYING for ammo. Feel free to use more."
This is another achievement related to the level Red Meat. As you enter the butcher shop at the very start of the level, several enemies will ambush you. Take your time and carefully aim for their heads. Kill each enemy with a single headshot and the achievement will unlock just before you enter the large meat freezer.
Once you start this level make sure you keep killing enemies with headshots until the achievement unlocks.