Green’s Dictionary of Slang

(Aus.) a supposedly fake illness or incapacity, used to justify malingering, apparently by Italians, Greeks, Yugoslavs and others seen as lazier than ‘white’ Australians.

1982		N. Keesing Lily on the Dustbin 51: There are racist overtones to [...] the ‘Mediterranean back’, which denotes derisive suspicion about a back-ache and ‘Mediterranean gut-ache’, usually shortened to ‘MGA’ which is just as suspect as the back-ache.
1991		R.G. Barratt ‘The Isn’t Union Bashing, But’ in What Do You Reckon (1997) [ebook] Besides spaghetti marinara our overseas friends have introduced ‘Mediterranean back’.