Using "zombie apocalypse" as a generic, tongue-in-cheek stand-in for the "worst case scenario" is harmless. Using it to refer to specific groups of people is boorish -- if you disagree with people, do so on the basis of specific concerns (otherwise the zombie may be you -- check in the mirror).

That said, and purely for your amusement, I can't help but relate this gem, which I believe I purloined (appropriately) from a zombiehunters post somewhere:

Leader: What do we want?
Mob: Brains!
Leader: When do we want it?
Mob: Brains!