Green’s Dictionary of Slang

odd, strange, eccentric.

1967		C. Cooper Jr Farm (1968) 99: I didn’t hear a thing that doofus little guy said.
1975		G. Underwood ‘Razorback Sl.’ in AS L:1/2 55: doofus ‘odd, strange’.
1987		(con. c.1967) J. Ferrandino Firefight 18: A doofis guy from North Carolina [...] None of us believe he’s fuckin’ human.
1997		‘Q’ Deadmeat 50: I can’t be dealing with those Dufus Pixel heads.
2004		J. Ellroy ‘Hot-Prowl Rape-O’ in Destination: Morgue! (2004) 260: Donna does doofus TV. She’s an on-call oncologist with a loser love life.
2021		J. Ellroy Widespread Panic 12: Central Division. The doofus day watch.