The depictions of blood boiling and people swelling up is Hollywod myth (Total Recall, Moon 44). It looks good on the big screen but it's not true in RL. Nor is the idea that some movies have (Red Planet, Mission to Mars) that people would instantly freeze. As long as you moderated your breath, it wouldn't be sucked from your lungs, well actually it blows out from your lungs, and you might be likely to blow off involutarily too. What would probably be the most dangerous, is that if you actually held your breath rather then allowing the excess to escape, the gases in your lungs would expand and could rupture them, causing an air embolism similar to what a diver can experience from rapid ascention while holding their breath. Depending on what time of the lunar day it was, the surface could freeze or fry your feet pretty fast, and you're get a quick sunburn from the extra UV. Of course the biggest trouble would occur when you breathed out the last of the air, and then tried to breath back in, there'd be no air. That would mean that you'd have about 3 minutes all up to think about how you're about to die before your body ran out of oxygen and you collapsed unconscious. The reason that the body wouldn't explode or boil is simply that its stronger than that. The skin is a good pressure vessel and there isn't a lot inside it to force its way out, or in. Fluids are all kept well enclosed inside the body and so won't boil off at all, though I'd suspect that your eyes and mouth would dry up quickly as these exposed fluids evapourated. Once you were dead, your body would decay due to the UV light damaging the proteins in it, and there is likely to be some decay from bacteria in the body starting to break it down. I suspect it'd slowly dry freeze and then become dust. I suspect that the heat and cold cycles of the lunar surface wouldn't be good for it either, frying your corpse like a steak during the day and freezing it solid during the night. That would destroy all the cells on your body, so with the drying effect of the vaccum, and the UV, I doubt it would last more than a few months at the most.
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