This is an expression to indicate whacking off (hence whack-off-ia). The bank part comes into the picture because every time you whack off, you usually deposit something.
John: Hey Paul, you spider monkey, have you been wanking all night again??
Paul: Hush John! Don't say it loudly. But yeah I made a large deposit at Whackoffia Bank last night.
A quaint but usefull Australian term of excitement. Mostly used by Australian men over the age of 80 and only after a good lie down before 3pm. Etymology uncertain but was in common usage before Twitter.
When you fail at something in life (eg. failing an exam or not getting a job), go home and spend an hour just standing in the shower, propping yourself up against the wall with your eyes on your feet.
Caleb knew the only thing to do after he didnt get prefect was take a failureshower.