Symptoms of lethal neutrino radiation in a hypothetical scenario Core collapse supernovae release the majority of their energy in the form of neutrinos. According to an XKCD What If, the neutrino radiation alone from a supernova at a distance of just 2 AU would be sufficient to cause lethal neutrino radiation poisoning.
Hypothetically, if this were to occur and only the neutrino radiation was present (with no stellar envelope swallowing you), what would the actual mechanism by which it kills be? Would it be through double strand DNA breakage as is the case with gamma radiation, or something else?
 A: The most common interaction of neutrinos with matter are reactions like:
$$ \nu_e + n \to e^- + p $$
or likewise for the $\mu$ and $\tau$ nutrinos creating muons and taus.
The majority of the energy of the incoming neutrino is carried away as kinetic energy of the electron so the result is a high energy electron. You can also get elastic scattering of the neutrino from an electron and again the result is transfer of kinetic energy to the electron.
For the unfortunate human caught in the neutrino shower there will be two consequences. The neutrino interaction changes the atomic number, e.g. carbon would change to nitrogen, which will destroy the molecule hit by the neutrino. The high energy electrons will also cause the usual damage caused by ionising radiation such as beta radiation.
The resulting damage is rather boring in the sense that it isn't different from regular radiation damage and the eventual cause of death would be the same.
A: It would wreck the DNA in cells that were actively dividing at the instant the radiation hit them. This means that any cells in your body that frequently divide would be killed. Those cells include the entire lining of your digestive system and the cells inside your bone marrow that produce red and white blood cells. This includes the different types of white blood cells that facilitate your immune responses.
So, your digestive system would be ruined, and with no immune function, you would quickly fall victim to massive bacterial infections. 
Within days, you would die in horrible agony. 
