[Neologic]

Apparently, the temperature differential between your body and the liquid nitrogen is so great that the radiant heat from you hand causes the stuff to instantly boil and forms an insulating layer of gas between them.

You are referring to the Leidenfrost effect. It's really quite fascinating and you can do more than hold a ball of liquid nitrogen in your hands. It's even possible to dip your hand into molten lead or to gargle liquid nitrogen, if you know what you are doing. See this page for some interesting discussion and cool photos of the above.

[Drango]

It's even possible to dip your hand into molten lead or to gargle liquid nitrogen,

Just wondering out loud...how was the first idiot to try this?