Green’s Dictionary of Slang

an eccentric, foolish or gauche person.

1971		Current Sl. VI 4: Dufus, n. A stupid, foolish, unconventional person.
1977		L. Heinemann Close Quarters (1987) 57: Dufus would sit there jacking his jaw till we were out of earshot.
1989		(con. 1968) W.E. Merritt Where the Rivers Ran Backward 24: Toss it out in front of yourself, dufous, so’s you don’t get shot, too.
1990		S. Morgan Homeboy 231: If that dufus were conscious [...] he’d wish our marital status was his biggest headache.
1997–2001		Online Sl. Dict. 🌐 duffis n 1. a strange person. 2. an unintelligent person. (‘Dave is such a duffis at times.’).