Gareth Morgan has hit out at New Zealand First leader Winston Peters, saying the Acting Prime Minister "represents all that's sick in New Zealand politics".
It comes after NZ First celebrated its 25th birthday, and Mr Peters took the opportunity to say the party had been more successful than other minor parties.
"We've seen political parties formed in recent times, backed by millions of dollars and big ideas, that have collapsed without the support of everyday New Zealanders," Mr Peters said.
The comment came shortly after the deregistration of The Opportunities Party (TOP) - the party Mr Morgan started.
On a Newshub tweet referencing the story, Mr Morgan fired back at Mr Peters, saying: "Tenure is not political success".
"To have been part of the [establishment] that's overseen rising inequality, stagnant productivity and [environmental] destruction for 30 years, Peters is a disgrace, champion of the largest intergenerational theft NZ's seen, represents all that's sick in NZ politics".
It's no secret the two don't get along. Last year, they exchanged a war of words at Rātana Pā.
Mr Morgan attacked the New Zealand First leader, calling him an "Uncle Tom" and not supportive of the Treaty.
"His Cheshire Cat grin can't disguise the fact his party is selling Māori down the river," he said.
Mr Peters didn't take that kindly, saying: "It's been a long time since I've been mauled by a toothless sheep."
He then called Mr Morgan a "thinned-down version of Kim Dotcom" and said he'd been coming to Rātana for four decades rather than "driving around Mongolia on a motorbike".
Mr Peters has been contacted about Mr Morgan's latest comment, but did not respond before deadline. This story will be updated with any response.