Green’s Dictionary of Slang

border n.

SE in slang uses

In compounds

border brothers (n.) [cf. bato n.]

(US prison) Mexicans.

2000

Other Side of the Wall: Prisoner’s Dict. July 🌐 Border Brothers: Mexican nationals.

border ruffian (n.)

(US) a native of Missouri.

1865

in B.L. Ridley Battles and Sketches of the Army of Tennessee (1906) 460: The North Carolinians are called ‘Tar Heels;’ [...] Missourians, ‘Border Ruffians’.

In phrases

over the border

outside Greater London.

2000

J.J. Connolly Layer Cake 66: From over the border, over the state line, over the M25.