I once drove with expired rego, the car was my older brother's Sigma.
Parked into Autobarn carpark in Crimebourne, cop car drove towards me in hurry, they tell me the rego is expired I didn't realise until they showed me in-board computer.
My brother decided he could piss off to other side of Australia without telling me the rego is expired.
$537 fine, no demerit points and he let me off for no P-plates when I was a P-plater (d'oh!), sent numerous of angry text to said brother forcing him to pay the fine.
My parents suggested me to contest the fine so I wrote the letter explaining my brother is a twat and decide to piss off to other side of Australia for 2 weeks holidays and didn't bothered to pay the rego.
A week or 2 later, they sent me a letter stating they won't pursue the fine.
So, that was my story of the saga of driving around without rego, after that I made sure I paid the rego a week earlier and at Vicroads (don't trust online payment and post office to make one on time).