Green’s Dictionary of Slang

lemon spread n.

[rhy. sl.]

(Aus./N.Z.) the head.

1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 35: Lemon Spread Head.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 106/2: lemon spread n. the head.