Free Love
In the level "Set the Controls for the Heart of the Negativatron" You'll find a broken arcade machine with a sackbot trying to fix it. Activate the machine and input the Konami Code (Up Up Down Down Left Right Left Right X O) and the arcade machine will explode revealing a set of numbers (3733 5683) It spells "Free Love" on a land line phone

THIS IS A EASTER EGG, NOT A CHEAT.