A mental illness that usually appears in pre-adolescent boys who have not yet developed musical tastes, after they have first played Guitar Hero. Symptoms include the notion that they can play guitar (even though most have never actually seen a real guitar), only listening to songs from Guitar Hero, not knowing the history or even the names of the band members of the bands those songs are from, lumping all of Classic Rock, Hard Rock, Heavy Metal, Alternative, Punk, etc...into just "Rock" (and not knowing what any of the genres are in the first place), and the belief that they will gain enlightenment/go to heaven/become operating Thetans/whatever if they can play "Through The Fire And The Flames" on Expert.
Remedies may include forcing the subject to go and listen to music not included in Guitar Hero, and for the love of god, keep them away from DJ Hero.
13 Year Old: (Listening to Jimi Hendrix)
Older Brother: "Oh, I didn't know you liked Classic Rock."
13 Year Old: "What's Classic Rock?"
Older Brother: ...
13 Year Old: "Well, Jimi Hendrix is a pretty good band, anyway..."
Older Brother: (Facepalm)
Older Brother: (Later) I think my brother suffers from Guitar Hero Syndrome.
Paul: Sucks man.