Green’s Dictionary of Slang

1. a general term of contempt, e.g. a fool, an incompetent.

c.1943		S .J. Baker Aus. Vulgarisms [t/s] 8: fartarse: A dithering, aimless person.
1946		K. Amis letter 15 July in Leader (2000) 79: *FARTARSE.

2. (Aus.) one who constantly breaks wind.

1985

‘Thommo’ Dict. Aus. Swearing & Sex Sayings 42: FART ARSE — A person who farts continually day and night without showing the slightest sign of shame or embarrassment.