How many neutrinos would it take to kill you? Of course, there are many different kinds, so let's assume:

*

*they'rre all standard $v_e$.

*they all intersect your body in random places.

*they are going at say, 10% of c (about accelerator speed). 

the standard target for a lethal dose is 50% of human adult subjects dead, either immediately or from complications (which is more likely with neutrinos as they have a small chance each of weak-forcing a neutron to beta decay, which can disrupt cellular function and give you cancer). How many would it take for this to happen?

 A: 
Each second there are about 100 billion ghostly solar neutrinos passing through the tip of your finger, and every other square centimeter of your body, whether you are indoors or outdoors, or whether it is day or night, and without your body noticing them, or them noticing your body. At night they go through the entire Earth before reaching you.

Neutrinos are quantum mechanical elementary particles, and the question, imo, to ask,because quantum mechanics is a probabilistic theory,  "how probable is it for a cosmic neutrino to interact with a nucleus in your cells and create a neutron interaction that will lead to a cancer cell which will develop to cancer"

For example the neutrinos produced in nuclear reactors with energy E=1MeV have a crosssection of order $10^{-44}$,
this corresponds to a probability of $10^{-18}$ to interact in a solid detector with the thickness of one meter,

The odds are against the cancer  happening as these numbers show.
Th physics reason this is so , it is because neutrinos are neutral,and interact to first order  with the weak interaction which means they have a very small probability to interact.
