"Okay, the particle death ray worked in counterclockwise mode, next we'll test the antimatter death beam clockwise."
"Then you'll destroy the world?"
"No no no, these were just the preliminary tests. Then we move on to the full tests where we being the beams up to full power, but don't let them collide..."
Actually, though, I've read papers that say they've narrowed down the Higgs Boson's mass to a range where vacuum collapse would be a purely local event. Of course, since they're not actually sure that the Higgs Boson even *exists*, you've got to take that with a grain of salt. They could still destroy the world in some way they haven't predicted, because the argument about cosmic rays is leaving out some details, like that while each collision is less energetic than a cosmic ray, they plan to do billions of collisions in a tiny time frame, which could heat the area of collision up to levels that cosmic rays don't reach.
Really, I don't think anything catastrophic is going to happen. The LHC is impressive and all, but it's something that can be built on earth using resources found on earth, so it shouldn't be enough to hatch the egg.