Green’s Dictionary of Slang

Bahamas n.

also Barbados

In phrases

go to the Bahamas (v.) [the distance of the Bahamas from the mainland]

(US Und.) to be sent to solitary confinement, thus down in the Bahamas, in solitary confinement.

[US]Bentley & Corbett Prison Sl. 10: Going to the Bahamas Being sent to the ‘hole’ or isolation unit.
[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 12/1: Bahamas, the n. pl. the solitary confinement cell, the secure unit: 'x is down in the Bahamas for the week.' [ibid.] 13/2: Barbados n. = Bahamas, the.