Mark McGowan privately described Clive Palmer as "the worst Australian who's not in jail" in text messages revealed in court during their defamation trial.
The West Australian premier was grilled on Wednesday about his personal communications regarding Mr Palmer while facing cross-examination in the Federal Court in Sydney.
Mr Palmer is suing Mr McGowan for defamation, claiming public comments - including labelling the Queensland businessman the "enemy of the state" - had damaged his reputation.
The premier has lodged a counter-claim that he was defamed in several of Mr Palmer's interviews and statements.
Mr Palmer had sought up to $30 billion in damages over a 2012 decision by the former Liberal state government not to assess his proposed Balmoral South iron ore mine project.
The McGowan government introduced extraordinary legislation in August 2020 to prevent Mr Palmer from suing the state.
Mr McGowan was questioned about text messages he sent to media mogul Kerry Stokes, the chairman of Seven West Media.
The premier messaged Mr Stokes on August 11 alerting him to the introduction of the amending legislation.
Over the next three days, his daily newspaper The West Australian ran front pages variously depicting Mr Palmer as the movie villain Dr Evil, a cane toad and a mosquito.
On August 14 when the legislation passed, Mr Stokes messaged the premier to congratulate him.
"Thanks Kerry. I was asked about those marvellous front pages today ... I appreciate the support enormously," Mr McGowan replied.
"All the mealy-mouthed tut-tutting by some people about Palmer's 'rights' makes me sick."
Barrister Peter Gray SC suggested it reflected an intense hatred of Mr Palmer, whom the premier wanted to attack and discredit "as often and as harshly" as possible.
"I don't like Mr Palmer. I can't stand what he does," Mr McGowan replied.
The court was shown messages between the premier and WA attorney-general John Quigley, who will also give evidence in the trial.
Mr Quigley labelled Mr Palmer a "big fat liar", saying he was "looking forward to dumping on Palmer in statesman-like way".
At one point, Mr McGowan wrote in reference to Mr Palmer: "He's the worst Australian who's not in jail."
Asked whether that remained his view, Mr McGowan said he had probably been exaggerating.
"I suspect there are worse Australians out there who are not in jail ... people who have committed crimes and haven't been found guilty," he said.
A High Court challenge against WA's hard border by Mr Palmer and his company Mineralogy failed in 2020.
Mr McGowan agreed that various barbs against Mr Palmer, including labelling him an "Olympic-scale narcissist", were intended to pressure the federal government into withdrawing its short-lived support of the case.
He acknowledged his description of being "at war" with Mr Palmer was a prepared line which he repeated verbatim from talking points.
Mr McGowan has claimed public statements by Mr Palmer contributed to crazy behaviour, including death threats against him and his family and a woman ramming her car into a power pole outside his home in November last year.
WA Police said the woman was a drink-driver and the location was a coincidence.
But Mr McGowan, under questioning from Mr Gray, maintained it was a deliberate act involving an anti-vaxxer.
"The woman in question, when my children went out to help her, screamed anti-vax sentiments at them and then ran off into the darkness," he said.
In his evidence last month, Mr Palmer said he was scared because provisions in the Balmoral South legislation protected the government from criminal prosecution.
Referring to the fictional character James Bond and his "licence to kill", Mr Palmer told the court: "I didn't know what the limits might be."
