Do you know ghouls from goblins and ghosts?
"crazy, eccentric," 1935, variant of whacky (n.) "fool," late 1800s British slang, probably ultimately from whack "a blow, stroke," from the notion of being whacked on the head one too many times.
(also wacked-out or wacko or whacked or whacked-out) Crazy; eccentric; nutty: You think I'm going wacky?/ annually collects whacky accidents/ the most wacked-out cop game anybody had ever seen any cops play/ the wacked-out hustler who talks Winkler into running a call-girl service out of the morgue/ She tried to convert me to her religion! She was whacked
[1935+; fr British dialect whacky, ''fool,'' attested fr the early 1900s; whacky, ''a person who fools around,'' is attested in British tailors' talk fr the late 1800s; perhaps fr being whacked over the head too often; perhaps influenced by whack off ''masturbate,'' and semantically akin to jerk]