Green’s Dictionary of Slang

apple knock v.

[apple-knocker n.]

to act the yokel, to behave in an unsophisticated manner.

[US]Berrey & Van den Bark Amer. Thes. Sl.
[US] in R. Butterfield Sat. Eve. Post Treasury (1954) 23 Nov. 480: You’re crazy, you damn apple-knocking liar!