Definition of "doofus"

Nichols had called Bonilla a doofus who was too damn stupid to realize that he was being taken by a hooker with a convincing sob story.Even if Steve was a doofus, Nichols and Rand were quite willing to work for him as long as he had money.

1998, Ann Rule, “In the Name of Love”, in In the Name of Love and Other True Cases: Ann Rule's Crime Files Volume 4, page 185

They weren't excited about acquiring new information; they were relieved to find out they aren't the only doofuses (or maybe the word is "doofi") in the world of rusty machinery.

2000, Roger L. Welsch, Love, Sex and Tractors‎, page 16

Being too young to attend a show on Bowie's 1983 Serious Moonlight tour, I did what any underage doofus would do. I bought a concert T-shirt – three-quarter-length blue sleeves, image of Major Tom himself on the front.

2005 October 17, Kevin Amorin, Mewsday, quoted in 2007, Troth Wells, T-Shirt, page 14

"I never seen so many doofuses in one place!""That's doofi, Krakauer. Sorry to correct you."

2009, B. K. Holway, When Jack Was with Us‎, page 115

"No problem. You get a bimbo babe who's engaged to a doofus who will fall for the virgin birth line and still marry her. […] However, I don't think a doofus fiancé will be hard to find; there's no shortage of doofuses on the earth."

2014, G. Richard Bozarth, Bible Tales for Ages 18 and Up‎, page 219