Interestingly enough, "biffin" is also a little-known Australian slang-word for the perineum, the bit of - for lack of a better term - squiggly skin between your anus and your genitals. I first learned it when a friend of mine recited this song...

Between your balls and your bum is your biffin,
It's a place where you shouldn't be sniffin'...


Charming, no? This friend's father is a gyno, so he has plenty of other little gems of wisdom concerning all manner of interesting, obscure areas of the anogenital region.

As you can imagine, I was quite shocked when I learned biffin was also an apple treat. No so tasty anymore, ey, kiddies?