This has been explained by Snopes here (as well as elsewhere) but I want to add a few little details that I found interesting.
The story goes that various news outlets reported that a “NASA engineer/scientist” had told Conan O’Brien about a NASA mastubation ban, whereas the idea of a ban and the reasoning behind it was actually put forward as a joke by Conan’s co-host Matt Gourley during a conversation with Smythe Mulikan ... Read even more
