From Wiki for those who are clueless:
"Guido" is a pejorative slang term for a young, lower class or working class, Italian-American or Italian-Canadian male from the urban Northeastern United States or urban Central Canada, most often New York and the surrounding area due to the large number of Italian-Americans living in the area. The Guido stereotype is often portrayed as humorously thuggish and overtly macho attitude and an unyielding pride in his Italian ancestry.