is a delightfully coarse traditonal Australian
slang exclaimation of disappointment. It is dervived from the colloquialism "to spew", meaning to vomit
Most Aussies who'd use this term in day-to-day language would drop the trailing g, and pronounce the word spewin'
Bruce: "Aw mate, waddya mean you missed out on Grand Final tickets?!? Spewin'..."
Davo: "Yeah, mate, spewin'..."