But when you get about 80 young people at an 18th birthday party there will nearly always be some minor dramas before the night is over.

Mostly, when the dust settles, there will be colourful stories to be repeated at later family events with a collective roll of the eyes.

Not this time. It was more than five years ago but the chain of events from that night left two families traumatised and the guest of honour the victim of a wicked injustice.

There were mistakes that night. Security did their job by ejecting gatecrashers but there was probably too much booze too freely available to kids too young.

Malcolm* wouldn't be the first teenager to enjoy a few too many on reaching the legal drinking age. Looking back he started too early and finished too late.

Nor would he be the first to slip away to an unlocked bedroom with his girlfriend for their own private celebration.

They had been an item for months. They went to the same school where she was a year 9 student and he was in year 12. Carol* was 14 (nearly 15) and he was 17 – until the day before the party.

That one day would make all the difference because by the Saturday he was 18 and in the eyes of the law no longer a kid. She was 14, which made her a child.

While she was a consenting partner in whatever happened in the bedroom (there were no allegations of full-on sex) that 24 hours meant even though they were girlfriend-boyfriend he was an adult committing a sexual offence against a minor.

Carol's parents had told their daughter they were concerned about the age difference but she assured them all would be fine. Despite their doubts they finally agreed she could go to the party on the strict understanding they would pick her up at 11pm.

When they arrived she couldn't be immediately located until Carol's mother found her under a doona with Malcolm, her clothes in disarray. She shooed her daughter downstairs and into the family four-wheel-drive loudly declaring, "You are never going to a party again!"

When her father learnt of the circumstances he became outraged at Malcolm and his parents, blaming the latter for lack of supervision.

He wanted to confront the parents and the night might well have turned violent if the security hadn't stepped in.

Then what would have been an embarrassing end to the party became an official police investigation. The girl's understandably livid father drove straight to the nearby police station to lodge a complaint, believing (wrongly) his under-age daughter had been manipulated into having sex with the older boy.

A few days later Malcolm was formally interviewed and later charged with sexual assault. The charge sheet alleged the "indecent act" consisted of "kissing, cuddling and laying naked".

In her statement to police Carol said, "I have never had sex" and "we didn't exactly do anything".

Here is where the law of unintended consequences kicks in. Since 2004 Victoria has had the Sex Offenders Registration Act designed to enable authorities to monitor potential predators after they have served their sentences.

This is a perfectly sensible move to protect the community but when someone like Malcolm is caught in its web then something is radically wrong.

In March 2012, Malcolm pleaded guilty before a magistrate to committing an indecent act against a child under the age of 16.

According to news reports at the time the magistrate said, "You were an adult and she was a child.

"The gap in your ages was not great. You had been in a relationship with the girl for some time. Obviously you have a lot of remorse for what you did ... You are, in general, a fine upstanding citizen."

He was given a 12-month good behaviour bond and ordered to pay $400 as a charitable donation. This, you would think, was a fair result. No conviction, a slap on the wrist, a lesson learned and honour restored.

Except as this was classed as a sex offence by an adult against a child the magistrate had no option under the mandatory terms of the act but to place him on the Register of Sex Offenders for eight years.

The stupidity is that magistrates and judges have discretion when dealing with sex offences against adults. Which means a convicted rapist will be placed on the register only if it can be proven beyond reasonable doubt that "the person poses a risk to the sexual safety of one or more persons or of the community".

The truth is no one – not the police, the courts nor the prosecutor – think Malcolm will reoffend, is a predator, or is a risk to anyone. Yet he is lumped in with child molesters, internet predators, serial rapists and assorted violent perverts.

To make matters worse everyone knows the act is flawed.

Just over a year after the doomed party the Victorian Law Reform Commission completed a report into the act. It exposed this exact problem and recommended change to the mandatory component to avoid these sort of cases. "A clear exception is a young person who is involved in an ongoing, sexual relationship that would not have constituted sexual offending but for the age of one of the parties involved. In such cases, the court would make an individual assessment."

The Law Reform Commission reported there were 4165 people on the list in December 2011 with the number likely to rise to 10,000 by 2020. This is an impossible number to monitor and if the system is gummed up with cases such as Malcolm's it is increasingly likely offenders who are a risk will slip through the net.

So not only is it unjust but ineffective and counterproductive. Which means while we are concentrating on sardines we may miss the sharks.

According to Pat*, Malcolm's mother, the registration of her son has been catastrophic. She says he was sacked from his job without explanation shortly after the court case and was sledged on sporting fields to the point where he stopped playing football and cricket.

He abandoned his sport administration degree as he could not complete the fieldwork because as a registered sex offender he is banned from working with children. He couldn't umpire junior cricket games and his long-term plans to become a sports teacher have been destroyed.

"For months he was so depressed he just stayed curled up on the couch," she says.

He has to report the details of any cars he drives, the names of clubs he was connected with, which have  child participants and even provide details of his internet server.

He feels harassed by the police and victimised by the courts. "All this is because of a kiss and cuddle between a boy and his girlfriend," Pat says.

The one-time extrovert has become withdrawn and has not been out with a girl since his 18th birthday. Strangers think he is shy. His family say he is crushed.

Pat says when he went interstate with his father to watch North Melbourne play Sydney in a final he was told by a policeman he was in possible breach because he was out of the state for more 48 hours.

He had a chance to get a job driving taxis but was refused a licence because – you guessed it – he is a registered sex offender.

Father Ron* says some in the town hear the word "sex offender" and conclude his son is a rapist.

"What he did was silly but what has happened to him is so unfair. He is not the only one. There are adolescent boys who have had their lives ruined by what is a badly drafted law.

"I can't believe this law was designed to smear kids who are not criminals."

The commission says the one-size-fits-all approach in cases such as Malcolm's just doesn't work. "Replacing automatic inclusion in the register with a process that allows for individual assessment of the offender is highly likely to enhance the effectiveness of a scheme that places a great strain on the resources of Victoria Police and the Department of Human Services."

And Malcolm's is not an isolated case.

Law Reform Commission chairman, former Supreme Court justice Philip Cummins, told us: "The commission is not able to comment on specific cases. However, when the commission was reviewing the registration of sex offenders in 2011, we were told of and spoke to young adults (and their families) who had been registered as sex offenders although they posed little or no risk of reoffending.

"That was a factor in the commission's recommendation that statutory inclusion should be replaced by individual assessment of offenders, a position supported by most submissions."

In other words the law as it stands is utter crap.

The trouble is there are votes in getting tough on sex offenders and so who wants to be seen as weakening existing laws?

Except this isn't a tough law, it is a just a bad one and it is time for politicians on both sides of the house to be brave enough to admit it.

*names have been changed