Deputy Prime Minister Chalerm Yubamrung vented his frustration on Friday over the cabinet reshuffle and challenged Prime Minister Yingluck Shinawatra to drop him from the lineup.
Mr Chalerm shocked senior police officers by turning a policy forum at the national police headquarters into a platform to attack the reshuffle.
One day after appearing to accept his fate amid reports that he would become the labour minister, the veteran politician confessed his true feelings to an audience that included the national police chief, Pol Gen Adul Saengsingkaew.
He accused Thawee Sodsong, secretary-general of the Southern Border Provinces Administration Centre (SBPAC), of lobbying former prime minister Thaksin Shinawatra and his sister to strip him of his role in charge of resolving southern unrest.
Despite overseeing efforts to resolve the southern conflict, Mr Chalerm kept putting off visits to the area for months on end before finally travelling there earlier this year.
He claimed Mr Thawee told Thaksin and Ms Yingluck a lie that police were unhappy with him because he had set up gambling dens.
The root cause, Mr Chalerm added, was conflict between the SBPAC and him over southern policy. He said he was left out of attempts to resolve southern violence despite being assigned by the prime minister to chair the command centre in Bangkok.
That included having the prime minister sign a document with Hassan Taib, the coordinator of the Barisan Revolusi Nasional (BRN), as the first step leading to peace talks between the separatists and government officials led by National Security Council chief Lt Gen Paradorn Pattanatabut.
He said he was never informed about the move, which he strongly opposed in any case.
"Pol Col Thawee never listened to me. [He] is a yes man," the deputy prime minister said.
He went on to lash out at Mr Thawee, saying he pleased only the southern Muslims but ignored the plight of soldiers working in the troubled area.
Mr Thawee bypassed soldiers and only listened to his team at the SBPAC, Mr Chalerm added.
Mr Thawee was a police colonel before moving to the Justice Ministry.
Mr Chalerm made no secret of his dislike for Mr Thawee, referring to him in a rude manner.
"Ai Thawee never respects me. That's okay. But he should respect other members too," he said, referring to officials working on southern issues.
"The current problem in the South that the government is facing is partly because of Ai Thawee."
The peace talks have come to a crucial stage as the government demanded in the latest meeting that the insurgents reduce violence during Ramadan. The BRN on Monday called for a troop withdrawal in exchange for such a pledge, something the Thai government totally rejected.
Mr Chalerm also challenged Ms Yingluck to purge him from her cabinet entirely but warned of the consequences.
"If the prime minister is not happy and wants to move me out, I don't mind," he said.
"But nobody wants to have a quarrel with Mr Samak [Sundaravej] and me," he said referring to the late former premier who, like Mr Chalerm, was known for his sharp tongue and bruising style. "Whoever does that, he or she is taking the wrong medicine.
"I don't care about being dropped. I'm happy to go back to being an ordinary MP. I've come this far because I've fought for it. I'm not a gigolo."
He also sent a warning message to the prime minister that politics was moving toward a "critical mode" because Ms Yingluck for two years has avoided confronting problems, such as the rice-pledging scheme, now under fire because of huge losses and corruption.
Opponents including the new white-mask group were trying to incite the red-shirt supporters of the Pheu Thai government to violence as a political ploy, he added.
Pol Gen Pracha Promnok is expected to replace Mr Chalerm as a deputy prime minister.