Green’s Dictionary of Slang

bobber n.2

[? bubby n.3 or ? it bobs up and down]

(Aus.) a female breast.

[Aus]‘Tit-Bits’ in Mess Songs & Rhymes of the RAAF 35: As this hobble-de-hoy, this frolicsome boy, / In her bobber sank thirty-two teeth.
[Aus](con. 1940s–60s) Hogbotel & ffuckes ‘Tit Bits’ in Snatches and Lays 12: [as 1945].