The AM Show host Duncan Garner has called on Marama Davidson to "get out of office".
The Green Party co-leader appeared on the show on Monday morning to discuss her party's commitment to raising benefits by 20 percent, but was unable to say how much it would cost.
Greens have no idea how much welfare overhaul will cost.
Ms Davidson said if New Zealand can spend $100 million of taxpayer money on the America's Cup, then it can pay its poorest a bit more.
"Too many people are struggling to make ends meet at the moment, and that's not good enough," she told him, but had no idea the costs involved.
"I am staggered by the lack of facts and detailed knowledge that she showed in her interview with me this morning," Garner said after the interview.
"No detail at all. She's exposed herself as being underdone at best, and completely incompetent at worst. It's called flaky. I wonder how much longer [co-leader] James Shaw can actually put up with this.
"She knew how much it cost for the America's Cup, but not about the welfare system which she wants to change. Honestly, get out of office. That's what I say."
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Garner also read out emails from the public, backing his view.
"That political interview - facepalm," wrote Gary.
"Duncan, that's five minutes you'll never get back. What a waste of space she was. Do we pay this woman?" asked Kevin.
"First time in Government for the Greens? Let's hope it's their last," said Lenore.
"How can any New Zealander have any faith in the coalition when someone as unprepared as Marama Davidson comes on your programme with no facts or figures, except to confirm what we all know - that this Government will need to raise more taxes to pay for their feel-good policies," wrote Grant. "What an amateur display by her."
Mr Shaw has previously defended his co-leaders uncompromising stance on controversial issues, such as using the C-word in public.
"It's extraordinary that the story has been about the language that Marama used rather than the death threats and rape threats she's received," he told RadioLIVE in August.
MPs label Marama Davidson's use of C-word 'disgusting', 'appalling'
Mr Shaw also stood by Ms Turei after she admitted to breaking the law in the 1990s to get more money while on the Domestic Purposes Benefit. Ms Turei ultimately resigned, but the party has retained her policy of boosting welfare payments.
The AM Show has asked Mr Shaw if he still has confidence in Ms Davidson.
Watch the full interview with Marama Davidson above.
The AM Show with Duncan Garner, Amanda Gillies and Mark Richardson, weekdays 6-9am on RadioLIVE and streaming live to the rova app on Android and iPhone.