Green’s Dictionary of Slang

virgin n.2

[note 1940s US Army virgin, a soldier who has yet to contract venereal disease]

1. (US Und.) a criminal with no convictions, thus the (lower) sentence allotted to such a criminal.

[US]‘John Eagle’ Hoodlums (2021) 133: Martin would get no virgin [...] Why endanger himself for the Federal rap?
[US]G.V. Higgins Friends of Eddie Coyle 169: Wouldn’t matter they was all virgins. Which they aren’t.

2. (N.Z. prison) a noice officer.

[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 198/2: virgin n an inexperienced officer new to a prison.

SE in slang uses

In compounds

virgin pullet (n.) [pullet n. (1)]

‘a young woman who though often trod has never laid’ (Jon Bee), i.e. no longer a virgin but not yet a mother.

[UK]‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 141: Pullet [...] a female barn-door fowl, which has not yet produced eggs. Young women are so denominated, occasionally; and sometimes we have ‘virgin-pullet, who though often trod has never laid.’.
virgin vault (n.)

(US campus) residence hall for females.

[US]Eble Sl. and Sociability 42: Alliteration marks [...] virgin vault ‘residence hall for females.’.

In phrases

born-again virgin (n.)

(US gay) a celibate homosexual man.

[US]R.O. Scott Gay Sl. Dict. 🌐 abstinence: 1. not taking part in sexual acts 2. not masturbating or denial of all sexual pleasure. Synonyms: born again virgin.
virgins’ bus (n.) [‘so named satirically in reference of the chief patronesses at that late hour’ (Ware), i.e. girls who have resisted male advances]

the last bus to run westward from Piccadilly Circus.

[UK]J. Ware Passing Eng. of the Victorian Era 257/1: Virgins’ bus (Peoples’, 1870). The last bus from Piccadilly Corner westward. So named satirically in reference to the character of the chief patronesses at that late hour. No longer runs – the tubes bowled over this vehicle.