During the "Road to Victory" level, you will come to a stealth part inside a building where you need to kill a blue boss. After gaining the washroom achievement in this section you'll want to go to the next area. In the next area, stay on top of the office area, using the ledges above it to sneak to the very end of the office section. When you reach the end of the office, you will find the copier inside the cubicle on the right hand side. Use your gun or explosives to blow it up, and unlock the achievement!