Green’s Dictionary of Slang

behind adv.

[behind n. (2)]

[late 19C+] ref. to the back of an object, spec. working as a bus conductor.

SE in slang uses

In phrases

all behind in Melbourne (adj.) [pun on behind n. (1)/SE behind]

[1940s+] (Aus.) fat, heavy-buttocked.

all behind like the cow’s tail (adj.) [pun]

[mid-19C+] late.