That's a new one, that's not the origin I've ever heard before. 3 different versions are on wiki
There are several folk etymologies for "pommy" or "pom". The best-documented of these is that "pommy" originated as a contraction of "pomegranate".[19][14][20][unreliable source?] According to this explanation, "pomegranate" was Australian rhyming slang for "immigrant" (like "Jimmy Grant").[21] Usage of "pomegranate" for English people may have been strengthened by a belief in Australia that sunburn occurs more frequently amongst English immigrants, turning those with fair skin the colour of pomegranates.[
Another explanation – now generally considered to be a false etymology – was that "pom" or "pommy" were derived from an acronym such as POM ("prisoner of Millbank"), POME ("prisoner of Mother England") or POHMS ("prisoner of Her Majesty's Service").[23] However, there is no evidence that such terms, or their acronyms, were used in Australia when "pom" and "pommy" entered use there.
Other theories are that they come from the use of "pom-pom" guns by the British in the First and Second Boer Wars, from a corruption of "Tommy Atkins", or from "Pompey", a nickname for Portsmouth
Either way Australians use it on a derogatory way without knowing where it came from probably because they have very little wit or imagination.
