Weasil,
from the aussie slang dictionary located at http://www.koalanet.com.au/australian-slang.html#D
Dinkum, fair dinkum : true, real, genuine ("I'm a dinkum Aussie"; "is he fair dinkum?")
personally I have used it here and there as another way of saying "are you/is it for real?"
It isn't usually used for swearing purposes
but could be perhaps construed that way depending upon the circumstances.