Rather similar to the phrase 'Couldn't organise a piss-up in a brewery' though used in even less amusing and more wearisome circumstances. Generally used to describe management or any cack-handed effort at leadership when the job ought to be easy for a small subnormal child to do, particularly in an actual slaughterhouse, where everything breaks down constantly. Or livestock never turns up and everyone waits relentlessly.
Not a funny phrase, just sad.
The job is fucked (has gone to shit) as usual. Whist observing a manager running arround like a blue arsed fly, utterly devoid of any intellegent suggestion or decision and with an impending audit looming:
Employee 1:"bloody hopeless this lot"
Employee 2: "aye man, couldn't organise a killing in a slaughterhouse"
both laugh mirthlessly and each simultaniously though secretly wonder what their lives are about.