goopus, n. — Green’s Dictionary of Slang

goopus n.

also goopus bird

[var. on goofus n.; plus the mythical goopus bird, which can neither swim, run nor fly]

(US teen) a fool.

1950		Salt Lake Trib. (UT) 30 Sept. 2.1: If one looks like a Goopus bird, walks like a Goopus bird, Acts like a Goopus bird... [...] The Goopus bird can neithe swim [...] run [...] fly.
1963		Kingsport Times-News (TN) 24 Nov. 82/1: The Hip Chick’s cat will know she’s no goopus and is really ginchy when she sports this skizzy snicker slicker.
1969		Summerfield Sun (KS) 9 Jan. 2/3: Teen Talk Glossary [...] Goopus — a dope.