Green’s Dictionary of Slang

baggyarse n.

also baggy
[SE baggy + arse n. (1); their stereotypically ill-fitting, new uniforms]

(Aus. prison) the lowest rank of prison officer.

[Aus]Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Baggyarse. Unranked prison officer. A probable reference to the perennial problem of ill-fitting, freshly issued uniforms. (Because of the sedentary nature of the work, time resolves this problem). Sometimes just baggy.