Bolonkin & Friedlander (2013) argues that it might be possible for "a dying dictator" to blow up the Sun, and thus destroy all life on Earth:

The Sun contains ~74% hydrogen by weight. The isotope hydrogen-1 (99.985% of hydrogen in nature) is a usable fuel for fusion thermonuclear reactions. This reaction runs slowly within the Sun because its temperature is low (relative to the needs of nuclear reactions). If we create higher temperature and density in a limited region of the solar interior, we may be able to produce self-supporting detonation thermonuclear reactions that spread to the full solar volume. This is analogous to the triggering mechanisms in a thermonuclear bomb. Conditions within the bomb can be optimized in a small area to initiate ignition, then spread to a larger area, allowing producing a hydrogen bomb of any power. In the case of the Sun certain targeting practices may greatly increase the chances of an artificial explosion of the Sun. This explosion would annihilate the Earth and the Solar System, as we know them today. The reader naturally asks: Why even contemplate such a horrible scenario? It is necessary because as thermonuclear and space technology spreads to even the least powerful nations in the centuries ahead, a dying dictator having thermonuclear missile weapons can [produce] (with some considerable mobilization of his military/industrial complex)—an artificial explosion of the Sun and take into his grave the whole of humanity. It might take tens of thousands of people to make and launch the hardware, but only a very few need know the final targeting data of what might be otherwise a weapon purely thought of (within the dictator’s defense industry) as being built for peaceful, deterrent use. Those concerned about Man’s future must know about this possibility and create some protective system—or ascertain on theoretical grounds that it is entirely [impossible]. Humanity has fears, justified to greater or lesser degrees, about asteroids, warming of Earthly climate, extinctions, etc. which have very small probability. But all these would leave survivors—nobody thinks that the terrible annihilation of the Solar System would leave a single person alive. That explosion appears possible at the present time. In this paper is derived the “AB-Criterion” which shows conditions wherein the artificial explosion of Sun is possible. The author urges detailed investigation and proving or disproving of this rather horrifying possibility, so that it may be dismissed from mind—or defended against.

Warning: the paper is published in an obscure journal by publisher #206 on Beall’s List of Predatory Publishers 2013, and I was unable to find confirmation of the authors' claimed credentials from any reputable sources with 5 minutes of Googling. It also has two spelling errors in the abstract. (It has no citations on Google scholar, but I wouldn't expect it to have any since it was only released in July 2013.)

I haven't read the paper, and I'd love to see someone fluent in astrophysics comment on its contents. 

My guess is that this is not a risk at all or, as with proposed high-energy physics disasters, the risk is extremely low-probability but physically conceivable (though perhaps not by methods imagined by Bolonkin & Friedlander).