As Bernard (kid with glasses), you will eventually pick up the Fork located in the "Break" room.
From the Main Lobby where you start the game, open/go through the double doors underneath the WELCOME banner. Then, go through the Swinging door (no need to open, just click on it) located just to the left of the fireplace.
Once in the "Break" room, pick up the Fork on the table in front of you. Then, open your inventory, click on the Fork, then on the Microwave on the right of this room.
Bernard will say "I'd rather not" while your achievement pops.
While you're here, you can also get "And Then the Universe Explodes" by picking up the two coffee pots and attempting to mix them. See my guide on this achievement for more details.
If you see a way to improve this guide or want further clarification, leave a comment! Thanks!