a clueless person, most always lacking even the most basic social skills. a doofus often thinks they are a bit smarter then everyone else.
when a doofus makes silly comments at the dinner table and everyone rolls their eyes they think everyone got something in their eye at the same time.
A doofus views defeating a 6 year old at a game of tic tac toe
as an accomplishment to be bragged about.
A doofus does not understand why you are not fairly impressed by this.