blonk, n. — Green’s Dictionary of Slang

blonk n.

[? echoic of a solid object, i.e. the fool’s head, hitting something hard]

(Aus. prison) a fool.

1984		B. Ellem Doing Time 187: blonk, a fool or dill.
1986		R. Spicer Mud & Stars 7: Right be-fucking-hind you, you stupid blonk.
1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Blonk. A foolish person.
2010		Brisbane News 26 May 3: [W] all know university graduates who are, as my father would say, blonks.