Ben Zimmer in Word Routes:
The movie's official website says of the title, “In Iraq, it is soldier vernacular to speak of explosions as sending you to 'the hurt locker.'” In fact, like so much American military slang, hurt locker (along with related hurt expressions) dates back to the Vietnam War.
In The Historical Dictionary of American Slang, Jonathan Lighter includes an extended entry for hurt in its military use, which he defines as “trouble or suffering, esp. deliberately or callously inflicted.” One common use of hurt that sprang up in the Vietnam era is in the phrase a world of hurt, “great trouble or suffering.” In “My First Day in Viet Nam Combat,” an Oct. 15, 1967 battle report in the Chicago Tribune, new recruit Russell Enlow wrote, “But now, as I drained the last drop from the fourth canteen, I realized what a world of hurt I would be in if that resupply chopper didn't show.”
Vietnam was a breeding ground for other hurt phrases, such as in the hurt locker, in the hurt bag and in the hurt seat, all defined by Lighter as “in trouble or at a disadvantage; in bad shape.” On February 21, 1966, an Associated Press article by John T. Wheeler appeared in many newspapers around the country, quoting a U.S. military adviser as saying, “If an army marches on its stomach, old Charlie is in the hurt locker.” (“Charlie is an American nickname for the Viet Cong,” Wheeler explained to readers not yet familiar with such slang.)