Mark Watney, in the movie The Martian, says that,
If the HAB breaches, I'm just gonna, kind of... implode.
The corresponding novel, by Andy Weir, says he will explode (as pointed out by @MikaelSundberg).
I think he will neither explode, nor implode, but simply die of cold and asphyxiation.
Can anyone scientifically explain what will happen?
PS: The HAB is a NASA designed habitat for humans on Mars.