This achievement is called "Warranty void if used" and is awarded for creating any customised weapon.
The earliest I got this was when I 1st entered the lifeguard station.
From a previous quest Sinamoi or whatever his name was gave me a Nail stick blueprint as a reward. The are many blueprints available throughout the game so there will be many chances for this.
Now for the nail stick it needed 2 x nails and a wooden stick of any kind so keep searching through bags, cupboards and lockers for materials and after enter the upgrade bench in the lifeguard station (or any other place you find one).
Go to the create tab and if you have the right materials you can create a molded weapon and the cheevo is yours.