The Mason-Dixon Line is a demarcation line along on the East Coast that separates four states: Pennsylvania, Maryland, Delaware, and Maryland.
I’ve been hearing this phrase used since I was kid, and adopted it into my own vernacular early on.
The speaker will make a statement, usually in reference to the superiority or inferiority of a person, place, or thing, and then end by saying “… south of the Mason-Dixon.”
“She’s the prettiest girl south of the Mason-Dixon.
“My grandma makes the best pork chops south of the Mason-Dixon.”
“He’s gotta be the biggest dude south of the Mason-Dixon.”
As a born and raised Virginian, I heard this phrase flung around time after time. The understanding of this phrase is confined to communities living around the Mason-Dixon line itself, as most people not from that region of the United States are unaware of what the Mason-Dixon line is. The phrase is hyperbolic, used to exaggerate and emphasize the statement one is trying to make. Viewing the phrase from an emic perspective, I can say that it is often employed in a comedic manner, often to make disparaging remarks about someone, such as “That has to be the ugliest shirt south of the Mason-Dixon.” The phrase’s meaning and hyperbolic nature is known to all in these regions, so one’s opinion or joke can easily be inserted into the phrase to augment their meaning. Much of the South also has a spiritual connection to the land. Their identities are tethered to the physical nature and landmarks of their home. This may be due to residual sentimentality over the Civil War and the lives lost on the battlefields in the South. Nevertheless, there are a multitude of phrases and bits of lingo in the South that pertain to landmarks and the features of the land that Southerners inhabit. While the Mason-Dixon itself isn’t necessarily in the South, the use of this phrase intrinsically identifies one as belonging to the South.