Green’s Dictionary of Slang

jaro n.

a telling off, a scolding.

1885		Bulletin (Sydney) 17 Jan. 6/1: If he comes up again, / It is perfectly plain, / He’ll be hooted / And booted, / Until he has scooted – / In fact the big man of Monaro / Will ‘cop’ what most people term ‘jar-ro.’.
1897		Otago Witness (N.Z.) 1 Apr. 51/3: If he goes betraying any of our signs, signals, or passwords he will get ‘jarrab’.
1914		E. Pugh Cockney At Home 62: ‘Oh, go ’way,’ she says. ‘I’ll prong yer!’ she says. Then I give her a bit of a jyro, till she squealed and bashed my ’at in.

In phrases

give jaro (v.)

(N.Z.) to scold.

1904		‘G.B. Lancaster’ Sons o’ Men 42: Cookie’ll give yer jaro ’f yur late fur supper [DNZE].
1937–84		Partridge DSUE.
1988		McGill Dict. of Kiwi Sl. 50/1: jaro to scold (Maori ‘whauraura’, to scold); eg ‘kid doesn’t pipe down soon I’ll give it jaro, by crikey.’.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].