A Californian youth or former-youth whose mind was irreparably damaged by the sudden and ongoing outbreak of dude-ery in the area, which has since spread across the nation as well as over borders.
Common symptoms include exponential decline in vocabulary and reading skills, as well as an near-inability to comprehend anything even remotely resembling a real language such as those spoken by people that have not yet succumbed to the terrible ravages of Dudetardation.
Dude 1: "Dude look at that dude over there, Dude! That dude's totally got some totally major dude points, bro!"
Dude 2: "Wickeddd Dude! Dude. He's totally stomping that bro's head over there, dude!!"
Uninfected friend: "Yeah... You guys have clearly become dudetarded. Peace out bros, I'm outie yo."
Dudes 1&2: "Duuude."
(Note: Apostrophes or any generally sensible punctuation would not appear in such sentences if a dudetarded bro or brolette were the one writing them down.)