With a "job", there is always someone else involved or else payment would not really be payment, would it? Similarly, the suffix-like term "job" added to anything implies that someone else is involved, eg. head job
, rim job
, hand job
(No, not JUST because one can not reach on their own). Masturbating ones self should not be referred to as a whack JOB.
For Christmas I got an Xbox from mum and dad, Halo 2 from my sister and a whack job from uncle Bill!