I've been doing quite a bit of reading and research on the etymology of the word "hack" and its off-shoots, but I can't seem to find any evidence of the first instance of the phrase "hack job." I've searched the OED, online etymology dictionary, etc. Anyone have any insights to share? Thanks!
Hack job has an interesting history. The sense of hack in play here probably originates with the oldest uses of the word as meaning "to cut irregularly or inexpertly." That usage dates back to Old English haccian, and thence to the mists of antiquity. It's not hard to see how the other senses of hack, many of which carry connotations of poor quality or amateurishness, would have emerged out of this definition.
Hack job begins to appear in the literature in the 19th and 20th centuries. Most of the early uses are from the 1920s or later, although I find one fascinating example in a book review published in 1837:
There is a freshness and talent about this unpresuming production which has exceedingly captivated our fancy. There is not a hack line in it : what a treat for a reviewer ! and a reviewer in these days, when one hack job succeeds another with such unremitting activity, that it almost seems, at the end of the season, as if we had read only one huge hack work.
As with most of the other early uses of hack job that I have found, the sense of hack being used here is that of the hack writer, who produces large quantities of mediocre writing because of the money it brings in, rather than because of inspiration or talent. Interestingly, this sense of hack is apparently completely unrelated to the ancient cutting/chopping definition: the OED relates it to an obsolete use of hack to mean a horse that draws a hackney cab, another form of drudge work. (Hackneyed, meaning trite or clichéd, is also related.)
Throughout the 20th century, the use of hack job to mean mediocre written work predominates. It takes on an interesting sub-definition around the middle of the century, when I begin to see the hack job label applied specifically to works that (in the opinion of the writer) constitute severe and sustained attacks on a person, belief, etc.--what we might otherwise call a hit piece. This usage pretty clearly borrows from the older, unrelated use of hack as meaning clumsy, violent cutting: the hack writer is hacking away at his target.
It is not until the 1990s that I begin to see hack job used to refer generally to quick, shoddy work in contexts that have nothing to do with writing or the creative process at all:
The Chinese sometimes cut a chicken into chunks, bones and all, before cooking it. It's a true hack job, like Kentucky Fried Chicken, but remember that the bones add to the flavor.
The broadening of hack job in recent years has no doubt been influenced by the senses of hack popular in computing, meaning variously "to break into a computer system" and "to write computer code for pleasure, or to derive pleasure from writing computer code." This is supported by the appearance around the same time of the phrase hack together (roughly meaning "to create or assemble quickly or inexpertly"), which was initially used only as hacker jargon but is today, I'm sure we would all agree, understood by a wider audience.
That hack job came to exist as an idiom was probably inevitable: woodcutting is a job, being a hack writer is a job, so it's hardly surprising that the term would arise eventually, and in fact it has probably been coined multiple times independently. The evolving use of hack over the years has unsurprisingly contributed to an evolution in the way we use hack job as well.