A person who obsesses over guitars and guitar related paraphernalia. This Person spends most or all of there time talking about guitar and famous Guitarist they barely take the time to actually learn how to play a song from start to finish. A large number of these people attempt to learn songs like 'stairway to heaven' by 'Led Zeppelin'. A guitar nerd will also obsess over a certain model or brand of guitar such as the Les Paul, Stratocaster or SG.
Guitar Nerd: I just bought a new Pedal for my SG.
Friend One: Ya that will go good with all your other pedals, amps and guitars you don't know how to use.
Friend 2: Dude you are such a guitar nerd!