Green’s Dictionary of Slang

oi n.

also oi oi

(N.Z. prison) a skinhead and thus skinhead culture in general.

[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 128/2: Oi adv. 1 (also Oi Oi) a skinhead 2 skinhead culture, values and ideology.