What any man in the agriculture business who grew up in the South says out loud while passing by a group of blacks or Mexicans laying sod. The term refers to a lack of intelligence of the aforementioned negros/hispanics.
-while passing by people laying sod
Father: "Green side up, boys"
Son: "Why'd you go n say that, daddy?"
Father: "Son, they blue-gummers so dumb they wouldn't know a book if it hit 'em upside the head!"