To cark it is a lovely piece of the Australian English vernacular meaning to die.

"If you jump off that dunny roof in to the yabbie-filled dam, don't come crying to me if you cark it."
"Did you hear? Johnny's stud merino carked it. He was found belly up in the shearing shed this morning."

Cark it is generally used in conversation only and is to be used as a more flippant way of referring to death. The sad passing of a local celebrity should not use the term "cark it" in reference - part of being an Aussie is that we are a down-to-Earth bunch of people, but still show respect.

Origins and tidbits
This is a tough one - very few reliable sources come up. A lot of references attribute it to the similar "carcass". Other sources point to the onomatopoeia of the death rattle or final breath, as used in Sir Gawain and the Green Knight using "cark" as the description of producing the phlegm from the throat.

"Cark it" is first referenced on Usenet on August 13, 1999 in as part of fanboy feedback referring to people... uh... "soiling" themselves when they die.