Green’s Dictionary of Slang

irrespective of gender, excellent, first rate.

1906		Sydney Morn. Herald 22 Feb. 2/5: [advert] GAILY THE TROUBADOUR sent down to Fitz’s for a Sunday jar of Boskerina Beer.
1907		Quirindi Herald & District News (NSW) 5 Nov. 5/2: [advert] Look at my Boskerina Beauties before you think of sending elsewhere for eggs.
1909		Truth (Perth) 16 Oct. 4/2: What’s wrong with ‘Dead Drunk’s Dazzlement,’‘Boskerina Bustup,’‘Sanginuary Splendiferousness,’‘Gor-blimey Gorgeousness,’ and ‘Blankey Bobby-dazzler,’ as a few additional spasm starters?
1910		Sydney Sportsman 16 Mar. 7/5: On the flute or on the lute he’s boskerina.
1926		Sydney Mail 14 July 12/1: ‘Bonzer’ may have come from ‘bon’ or ‘bza’; and ‘bosker’ perhaps was twisted out of ‘bosky.’ (There is also ‘boskarina,’ which is, I understand, the highest form of ‘bosker,’ but it is only rarely used).