masc. proper name, Italian, literally "leader," of Germanic origin (see guide (v.)). As a type of gaudy machoism often associated with Italian-Americans, 1980s, teen slang, from the name of character in Hollywood film Risky Business" (1983).
A gaudy macho type: Guido: a greasy, pimpy, open-shirted, hairy-chested, gold-chaindanglin' sleazoid/ It's not my fault I look like a Guido
[1980s+ Teenagers; the name of a character in the 1983 movie Risky Business]