What it means
To cark it means to die or stop working for good. You can say a person carked it, but it's just as common for cars, fridges, phones, lawnmowers, anything that gives up the ghost and stays gone. It's very Australian, pretty blunt, and usually tossed out with that dry, dark-humour shrug Aussies do so well.
Usage examples
"Poor old Jonno's ute finally carked it on the highway last arvo, he had to walk back to the servo in thongs, absolute shocker"
"The fridge finally carked it in the middle of summer, of course, with a full week of barbecues coming up."
"Old Bluey the cattle dog carked it at sixteen, a grand age, and the whole farm felt a bit quieter after."
"My phone carked it halfway through the festival, so I was just free-ranging with no battery and no clue where anyone was."
"Thought the mower had one more summer in it, but nah, it carked it after ten minutes and spat smoke everywhere."
Where it comes from
Broad Australian for dying, or for a machine conking out for good. Most likely from carcass, with a nod to the croak of a dying crow, cark cark. When the old ute finally carks it, or sadly when a person does, that is the end of the road.