Goof is a British dialect term, meaning a fool, a clown or an oaf]("Goofballed" is reminiscent of "nutmegged," which regrettably has nothing to do with nutmeg-qua-drug.) The entry before that is about the history of "johnson" (and more generally proper names; but see here) as genital euphemism. I was amused by the similarity of the first use Green gives:
In succession the word has meant 1 [1930s–50s] marijuana. 2 [1940s+] (drugs) a barbiturate, a tranquillizer; thus goofballed, under the influence of barbiturates. 3 [1950s] any sleeping pill. 4 [1950s+] a knockout drop. 5 [1950s+] a mix of cocaine and heroin.
Still based on goof, a fool, goofball has also meant [1940s+] (US) a silly, amusing, eccentric or insane person; in this sense it can also be used adjectivally.
1863 W. Cheadle Journal 2 Feb.: Bitterly cold; neck frozen. Face ditto; thighs ditto; Johnson ditto, & sphincture vesicae partially paralysed.to the opening stanza of the "Eve of St. Agnes."