I think that the idea that you're referring to is the worrying possibility that what we think of as the vacuum is not the true ground state of the vacuum. It could be in a state analogous to a supercooled liquid. All it would take would be a small patch of "real" vacuum to nucleate the collapse of the rest of our vacuum into the true ground state. If this were to happen, it would likely be worse than letting the beams cross in Ghostbusters.