Kill the Living! Eat their Brains! Braaiiinns!
The players are zombies, kicking down doors and eating brains. The "monsters" they're attacking are people, some helpless and some hazardous, with a few rogue zombies thrown in. The armor is whatever they've blundered across during their lurching search for brains.
So bravely the munchkins go forth, with mousetraps on their feet and a bowling trophy protecting their poor rotting heads . . . to level up, or to die. Again.