plot idea I came up with while half-asleep:
survivors in a nuclear zombie apocalypse, but the zombie-ness of the zombies is actually just a skin-condition from the radiation and cold. the protagonist "survivors" have tacitly agreed that everyone else they don't want to deal with is a zombie. the viewers discover this late, and the zombies are shown the way the protagonists view them (shambling and rotting). you can hint at the truth with scenes like:
they clear out a building of zombies. on the roof, they see one zombie and one human who looks a bit sunburnt, one male and one female. two "survivors" see the one of a gender they're attracted to as human and attractive. they attack the other (it's going to kill him/her!). they bicker after killing them, but agree both corpses look like zombies.
the protagonists enter a church (or better, a mosque), and see zombies sit in locations similar to how humans would sit during a service. a zombified religious leader runs up to them, groans for a few seconds and then starts just shoving them; by this time they're infamous for killing people.
the delusion finally breaks when they enter a store, converse with the shopkeeper (who appears afraid of them), then only some of the "survivors" realize at the same time that they can't afford to pay and that the shopkeeper is a zombie.
