Green’s Dictionary of Slang

pisswhacker n.

1. [1960s+] (Aus.) a cicada.

2. [1970s] (Aus.) something superlative.

3. [2000s] (Aus.) of individuals or objects, as a term of abuse.

4. [200s] (Aus.) something easy.

In exclamations

holy pisswhacker!

[2000s] (Aus.) general excl. denoting emphasis.