You need at least one coin for this achievement. You find coins by searching things layng around.
Go to "Highschool" and make you way to the room where the guitar is located (let Jack and Foxy stay in an other room with a blockade). Run around and try to destroy the chairs to make space for you to escape while gathering zombies. (NOTE: the astronaut zombies do not count) Try to block some windows and make sure at least one zombies stays out. Run in circles around the zombies while opening some windows to let more zombies in or let them just break the blockades until you have enough. then go to the window which is still closed and make sure the zombies follow you. Replace the blockade with the poo trap and let the last zombie in, to infect the others, then run to the music box and insert coin.