A witty line by Stephen Hawking, famous English physicist, about the infamous thought experiment proposed by Erwin Schrödinger. A modification of a quote often associated with Hermann Göring: "When I hear the word 'culture' I reach for my gun".
Amusing but cryptic, it could be referring to any of the following points.
1. If you know who Stephen Hawking is, you know he can't actually reach for a gun (well, unless he has something like the spring loaded punching gun he had when he guest starred in an episode of the Simpsons)
2. Reconciling Quantum Mechanics and General Relativity has been a significant and very frustrating problem for modern physics. Perhaps so frustrating it would drive one to violence!
3. The Schrödinger's Cat gedankenexperiment has been the source of an incredible amount of Modern Physics Abuse Syndrome, leading some people, even respected physicists, to weird metaphysical interpretations of the nature of the universe. (On the other hand, the Schrödinger's Cat experiment does exemplify some major philosophical problems raised by quantum mechanics, which are only slightly "resolved" if one adopts Feynman's well respected and useful, but nonetheless unsatisfying Shut up and calculate! model. See Mauler's Layman's Guide to Quantum Mechanics for a summary of four different models that don't simply dismiss the problems).
Regardless of which interpretation you take, the Quantum Mechanics that Schrödinger's Cat represents, which is beautiful mathematically and in how it can explain the world, causes great difficulties both in explaining modern physics to the general public and in reconciling it with the theory of relativity. This is particularly bad for a man like Hawking who works with black holes, where gravity and quantum effects are both significant!