University policy: if a gunman offers you his gun, refuse it
Discussion at the Volokh Conspiracy. This is pretty insane, even for academia.
The faculty manual at Virginia Tech covers situations where a gunman offers to hand his gun to a faculty member.
It instructs the faculty member to reject it: "Never attempt to disarm or accept a weapon from the person in question. Weapon retrieval should only be done by a police officer."
Check the comments. I turns out this is apparently a boilerplate provision at a lot of universities.