Wikipedia
Guido (ˈɡwiːdoʊ) is a slang term for a lower-class or working-class urban Italian American. The guido stereotype is multi-faceted. Originally, it was used as a demeaning term for Italian Americans in general. More recently, it has come to refer to Italian Americans who conduct themselves in a thuggish, overtly macho manner. The time period in which it obtained the latter meaning is not clear, but some sources date it to the 1970s or 1980s.