The Seattle Times reports that a man died after "cracking" his own neck in 1996, establishing that it is possible for an individuals to break their own necks. The paper lists the man's official cause of death as "cerebellar infarction."
According to Huffington Post, the most common injury from neck cracking is stroke caused by damage to the arteries in the neck. It points out, however, that such injuries are very rare. It also advises that there is little scientific evidence that shows that the action has any health benefit.
C. Claiborne Ray, a New York Times columnist, recommends a stretching routine in lieu of "cracking" the neck to avoid the risk of injury.