Greg Craven brings up Giant Mutant Space Hamsters in his excellent video, "How It All Ends", as an analogy for an unrealistic threat.
(Of course, if you find that video helpful you should have a look at his book, "What's the Worst That Could Happen? A Rational Response to the Climate Change Debate" and pass it along to people you know.)
What Greg missed, though, is the fact that many influential people actually believe in giant mutant space hamsters! Many influential people these days believe lots of silly things, including the silly idea that global warming is a conspiracy wherein the entire scientific community has sold out lock stock and barrel to malicious windmill manufacturers or something. But the foolish belief in the space hamster is perhaps the most widespread, influential and dangerous of the crazy ideas that are commonly believed.
Update: Scruffy Dan has more information and ideas about the GMSH phenomenon.