It could also refer to guitar center, a popular chain in the US for instruments. Keep in mind, when referred to as "Guitarded center", the person using the word is usually not fond of guitar center (Personally I don't mind the store, but many people dislike it).
" Ah...so he's guitarded now, right Jeffrey?"
2: Guitarded as in a person that lacks musical knowledge.
"Dude. You don't even know what a Fsharp/D chord is!? And you've been playing for three years? No offence, Mikey, but you're guitarded."
3: Guitarded as in "person that is poor at playing the guitar": " Says Mr. Jeffrey who's so guitarded that he can't even play the G chord!"
4: Guitarded as in a reference to the music store chain Guitar Center: "Mike, I'm sorry." "I'm sorry too, Jeff. How about we go kill some time at Guitarded center?"
How you feel after playing an extra long set or gig.
Some dude at a bar when you just finished your last set and are rollin up for the night-"Hey I love you guys man you really sound great! Say, I play guitar too, and I was wondering if you wanted to jam.
You - "Sorry man, I'm guitarded. Not tonight."
Normal Human: OK. I played Stairway to Heaven backwards on an actual guitar.
Guitarded One: So....?
Note: normally this is used only by the guitar player him/herself, as those in the vicinity are likely also too inebriated to notice the guitardedness.