Photo credit: David Monniaux, via Wikimedia Commons.
Well, thanks to the Leidenfrost effect, your hand doesn’t actually get seriously messed up (but don’t try it, anyway). You may have noticed the Leidenfrost effect whilst cooking with a really hot pan. If the surface is hot enough (much hotter than the liquid’s boiling point), water droplets ball up into little dancing beads instead of instantly evaporating. This is because an insulating vapor layer forms between the liquid and the hot surface, preventing the rest of the water from touching the hot surface. This slows the heat transfer between the two and thus prevents the liquid from further evaporation.

This also happens when liquid nitrogen comes into contact with a room temperature object, such as your hand. Check out this video for a demonstration: