a temperature or climate that is not conducive or favorable to negro and/or halfrican people. The actual temperature threshold is unknown, although it is commonly believed to be somewhere around 45 degrees fahrenheit (or below).
halfrican/negro: "Dang yo, it feels like sub-negro temperatures out here - I shoulda brought my coat!"
halfrican/negro's friend: "Dude, it's only like 40 degrees out here."
halfrican/negro: "Well, where I'm from we ain't used to no 40 degree weather!"