Oakley and his victim, 24-year-old Lachlan Hutchins, did not like each other. There was bad blood long before the fatal August 2019 stabbing in the southwest Victorian town of Portland.

The pair happened upon each other at the same pubic toilet outside the local Woolworths in the middle of the night.

Oakley had a knife on him and said he could hear Mr Hutchins' voice outside the cubicle door, Victoria's Supreme Court was told on Tuesday.

The latter man had seen Oakley's car as he walked up to the loo and shadow boxed as he waited. He swung a punch when Oakley came out.

In the ensuring struggle, Oakley stabbed his opponent five times, piercing his lungs and heart, until the man freed himself and ran.

Afterwards, Oakley texted a friend: "C*** I f***ing stabbed Lachy like six times."

In another text to someone else, he wrote: "Bro, I've one-upped you with Lachy. I stabbed him".

At home, Oakley used a grinder to break up the knife and disposed of the pieces in the scrap yard next door.

Meanwhile, Mr Hutchins' girlfriend and his friend took him to hospital, but he died.

The month before, the pair had met for a pre-arranged fight, Oakley armed with a kitchen knife and Mr Hutchins with a vacuum cleaner pole.

Nothing happened, but afterwards Oakley texted a friend saying, "I told him I'm going to stab him LOL".

Earlier that year, Oakley and Mr Hutchins came across each in the Woolworths car park.

They fought, Mr Hutchins threw a soft drink bottle at Oakley's car and Oakley took off after the man with either a wrench or a tyre iron.

After the fatal stabbing, Oakley turned himself in to the police and said he thought Mr Hutchins may have been armed.

"I know Lachy was out there. I could hear his voice and I didn't want to go out (of the toilet) because I knew what would f***ing happen," he said.

In a phone call from prison, Oakley said: "I genuinely wanted him f***ing dead".

He was originally charged with murder, but pleaded guilty to manslaughter.

Prosecutor Robyn Harper told the court Oakley had "essentially brought a knife to a fist fight".

Mr Hutchins' mother, Tania, said her heart was "missing a piece and that piece is my son".

"I can't get past what he would have gone through in the last moments of his life," she said in a statement to Justice Paul Coghlan.

Mr Hutchins' father, Brad, labelled Oakley a "poor excuse for a human being".

The slain man's daughter, who was six when he died, said she missed him taking her to the park and the pool.

"Things are not very happy as I don't have a dad like the other kids," she said in her statement, accompanied by pictures she drew.

In a letter, Oakley offered his "deepest regret and sincere remorse" to Mr Hutchins' family as they watched in court.

"Although it was never my intention to cause such serious injuries ... I blame no one else," the killer wrote.

Justice Coghlan decried knife crime, saying "the court is truly going to have to do something about the prevalence of the use of knives by young men".

Oakley has already spent 644 days in custody and will be sentenced at a later date.

Australian Associated Press