A retarded guido. Commonly used to refer to cast members of the MTV show Jersey Shore.
Masculine: guitardo(s). Feminine: guitardette(s).
Human Being: Hey, what are you doing today?
Guido: G.T.L. baby. Gym, tanning, laundry. You gotta do the guido handbook.
Human Being: Wow! You f*#%ing guitardo! No! Bad guitardo!