[antognini]

The mean free path of neutrinos through lead is around one light-year. So, taking the thickness of the body to be 1/2 a meter, you would expect the probability of any individual neutrino to interact with the body to be ~5 x 10^-17. So you'd ballpark have around a 20--40% chance that a single neutrino interacts with your body. It would probably cause a localized radiation burn. Detectable, but probably not lethal unless you got really unlucky with where it hit you.

[pfdietz]

The mean free path of much lower energy neutrinos in lead is about a light year.

The MFP of a 120 PeV neutrino in lead would be something like 10 kilometers, I think.

[cozzyd]

More like 100 km I'd think but yeah, the neutrino nucleon cross section gets much bigger at high energies