"Ocker" is an Australian slang term that can be used insultingly to describe someone perceived as uncultured, boorish, excessively vulgar, or stereotypically "bogan" (uncouth, unsophisticated).
It derives from "Oscar" (a generic Aussie name) and the suffix "-er." The archetypal "ocker" speaks broad Strine, drinks beer, wears a blue singlet and shorts, and embodies a caricature of 1970s working-class masculinity.
However, context matters:
Use with caution: it can sound condescending or classist, especially from non-Australians.