Green’s Dictionary of Slang

split-ass adj.

[ety. unknown]

(Aus.) unusual.

[[UK]A.S.G. Lee letter in No Parachute (1968) 1 Sept. 83: Another pink-cheeked Warbabe It’s amazing how young they come, and all now in R.F.C. maternity jackets and split-ass caps].
[Aus]W.H. Downing Digger Dialects 47: split-ass (adj.) — Unusual.