from Wikipedia
“Guido” (or “Gino”) is a slang term for a younger lower class or working class urban Italian-American. The Guido stereotype is often portrayed as humorously thuggish with an overtly macho attitude and an unyielding pride in his Italian ancestry.
In a wider sense (and not directly connected to the above term anymore) is the use of ‘Guido’ as a bouncer slang term for an obnoxious club-going male.
Um, unless you were joking that isn't the reference I was referring to.
Look up "Guido's hand" as a mnemonic for solfeggio. That'll do ya. :0)