Green’s Dictionary of Slang

(orig. US black) an odd person, an eccentric; a fool.

1955		N.Y. Times 25 Dec. SM10: Doofus lost every round from the third, but they gave him the duke!
1967–8		Baker et al. CUSS 108: Doufus / also Doufas /A person who always fools around. A person who always does the wrong thing. A person without much social or academic ability.
1975		G. Underwood ‘Razorback Sl.’ in AS L:1/2 58: doofusn Person of little or no judgement or common sense.
1983		(con. 1967) R. Eilert For Self and Country 177: He looked back at me. ‘You duffus.’ My face turned red as everyone applauded.
1983		N. Heard House of Slammers 212: They were the chumps, the doofuses, who only got chump change in life.
1994		J. Wambaugh Finnegan’s Week 231: Oops [...] I’m such a doofus when I eat stuff like ... what’s this called again?
2003		Mad mag. Sept. 16: Pick up rubber gloves for those occasions when you need to ‘pants’ some doofus with questionable hygiene.
2015		S. King Finders Keepers (2016) 43: Ellen’s a doofus.
2020		Twitter 16 Mar. 🌐 Harriet Walter is one of the three or four (perfectly charming) celebs I've met [...] and accidentally mildly insulted whilst seeming like a complete doofus.
2020		D. Winslow ‘Paradise’ in Broken 246: A real dildo, a born-again doofus.