Green’s Dictionary of Slang

a phr. appearing in various combs., meaning to be very obvious, very large, e.g. …cod’s ballocks, …dog’s ballocks, …a sore thumb, (Can.) …a shit-house in the fog.

1983		C. Knight We Shall Not Die 145: Even in plain clothes him stood out like a sore foot.
1993		Smith & Noble Neddy (1998) 232: Sometimes the surveillance police would stand at the bar drinking, trying to look inconspicuous. They stood out like dogs’ balls, drinking schooners and wearing desert boots. [Ibid.] 255: I couldn’t miss them – they stood out like dogs’ balls.
1998		R.G. Barrett Mud Crab Boogie (2013) [ebook] Look at that, thought Les, raising his camera. They stick out like dogs knackers. No they don’t; they stick out like Alpacas knackers.
1999		Observer Screen 15 Aug. 20: The other acts were crap, so I stood out like a sore thumb.
2003		McGill Reed Dict. of N.Z. Sl. 198: stand out/stick out like a country shithouse/tits on a bull Obvious or conspicuous. ANZ.