Pressure

"When astronauts take a leak while on a mission and expel the result into space, it boils violently. The vapor then passes immediately into the solid state, and you end up with a cloud of very fine crystals of frozen urine."—Straight Dope (link)

"When the breathing ventilation valve opened at a height of 168 kilometers, the gradual but steady loss of pressure was fatal to the cosmonauts within about 30 seconds. By 935 seconds, the cabin pressure had dropped to zero and remained there until 1,640 seconds when the pressure began to increase as the ship entered the upper reaches of the atmosphere. The extent of tissue damage to the bodies of the cosmonauts caused by the boiling of the blood during the 700 seconds they were exposed to the vacuum could have been misinterpreted initially as being the result of a more catastrophic and instantaneous decompression."—NASA (link)

"Four divers in a compression chamber system were suddenly decompressed from 9 atmospheres to 1 atmosphere. One of the divers was about to close the door between the chamber system and the trunk when the accident happened. He was shot out through the door and severely mutilated. The three others died on the spot. The autopsy results are described. The most conspicuous finding was large amounts of fat in the large arteries and veins and in the cardiac chambers, as well as intravascular fat in the organs, especially the liver. This fat can hardly have been embolic, but must have "dropped out" of the blood in situ. It is suggested that the boiling of the blood denatured the lipoprotein complexes, rendering the lipids insoluble."—Giertsen, et al (link)