DOOFUS

dimwit, nitwit, half-wit, doofus

(noun) a stupid incompetent person

Source: WordNet® 3.1

Etymology

Perhaps an alteration of earlier goofus (first attested in the 1920s), due to influence from Scots doof ("simpleton"). Scots doof is derived from Low Saxon doof ("deaf"), which has a secondary sense: "idiotic". The Low Saxon word is cognate with English deaf.

Some have proposed that perhaps dupe played some kind of role in the development of doofus as well.

Goofus appears to be a fanciful extension of goof, perhaps taking its ending from ignoramus. Goof likely originated as an alteration of the (now obsolete) English goff ("a clown")—compare English geek, which originated as an alteration of geck ("simpleton")—but any of its history prior to that is up for debate, and difficult to precisely trace.