Australian origin: No. As in yes, I take your point, but let's be diplomatic: no, you're absolutely wrong.
A: So is the stove that I fixed working yet?
H: Yes no one of the burners is still on the blink.
Australian origin. Refers to the "bum cleavage" displayed most commonly by builders on construction sites, as their shorts or pants "slip". Pants worn by males at the mid-buttock level.
See Builder's Bum
A: Check out that Builders Crack.
H: Nothing better than a bit of builders crack coming out of a noice pair of terry towelling shorts.