At least one real life mad scientist seems to believe this is indeed possible, and with technologies that are at least conceivable with todays understanding of science and technology.

ABSTRACT 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.

Alexander Bolonkin, Joseph Friedlander; "Explosion of Sun" http://www.scirp.org/journal/PaperInformation.aspx?PaperID=34277

Assuming Bolonkin is correct, you would need to introduce a massive amount of energy into a very small area of the Sun over a very short time frame to trigger this fusion cascade effect. We might believe that energy releases many times that the "Tsar Bomba" would be needed, but according to the calculations in the paper, as little as 0.5Mt. detonated deep within the Solar Photosphere. I'll leave you to check the math and other assumptions of the paper, but as a lower bound, it is rather unsettling to contemplate.

WARNING: While this post does point to a scientific paper there are a lot of doubts about the quality of that paper and how reliable it may be. The review process of the paper, credentials of the author and validity of the claims have all been questioned. Unless or until those questions can be answered any information from it should be used with caution.

At least one real life mad scientist seems to believe this is indeed possible, and with technologies that are at least conceivable with todays understanding of science and technology.

ABSTRACT 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.

Alexander Bolonkin, Joseph Friedlander; "Explosion of Sun" http://www.scirp.org/journal/PaperInformation.aspx?PaperID=34277

Assuming Bolonkin is correct, you would need to introduce a massive amount of energy into a very small area of the Sun over a very short time frame to trigger this fusion cascade effect. We might believe that energy releases many times that the "Tsar Bomba" would be needed, but according to the calculations in the paper, as little as 0.5Mt. detonated deep within the Solar Photosphere. I'll leave you to check the math and other assumptions of the paper, but as a lower bound, it is rather unsettling to contemplate.