Green’s Dictionary of Slang

1. a diplomat, who is immune from Aus. law [the koala is an officially protected creature].

1984

Partridge DSUE (8th edn) 658: since ca. 1945.

2. an unappreciative man [a pun on the phr. he ‘eats, roots/root v. (5a) and leaves’].

1976

D. Ireland Glass Canoe (1982) 30: She christened the Koala Bear, who eats roots and leaves.