I have just realised that an English expression for left-handers, which I will render as 'cacky-whiffy', is a phrase I have never seen on paper. Can someone elucidate?

mav,

This appears to be an even more derogatory insult than the "cack-handed" whence it apparently sprang. "Cack" is British/Australian slang for rubbish or excrement (I certainly have heard and used the term "bird cack" in my time) and "cack-handed" is slang for awkward, and thence, apparently left-handed (cf similar usage of French word for left "gauche" for awkward).

See http://www.peevish.co.uk/slang/c.htm
cack-handed also rated a mention in one of our threads here from July: http://wordsmith.org/board/showthreaded.pl?Cat=&Board=words&Number=3028

"whiffy" is cited at the same slang site as meaning "smelling unpleasant".

I'm sure you get the drift.