His behaviour this week ranged from extremely bad to typically bad to unusually circumspect.
His public attack on former Prime Minister Jenny Shipley for being a friend of China was conduct unbecoming of a Foreign Minister, even allowing for his personal antipathy over his former boss.
Her apparent crime – wrong as it turned out – was that she had written an op-ed for the People's Daily praising China and the Belt and Road Initiative.
Finance Minister Grant Robertson and Prime Minister Jacinda Ardern deserved to be furious with Peters this week.
A day before the Tax Working Group report unveiled its recommendations for a capital gains tax, Peters told The Country's radio host Jamie Mackay that farmers would not be affected by a capital gains tax – wrong as it turned out.
"When it comes to the farming community, they are in for the long haul and there is no way a capital gains tax would have any effect on them at all," Peters said confidently.
"Farmers don't buy farms to speculate …they buy it for permanence, they are part of the provinces, they don't do this stuff you see in Christchurch, Wellington or Auckland."
His comments could only have been based on one of three things: either he was apprising the public of an incredible recommendation by the Tax Working Group that farmers were to be exempted from an otherwise comprehensive capital gains tax; it was an audacious opening gambit of Peters' negotiation with Labour over the final shape of the CGT; or he didn't know what was in the report and was indulging in a little nostalgia from the 1950s, and seems the most likely.
Peters was evidently under the impression that a capital gains tax was going to apply only to short-term speculative sales.
In fact farms, except for the family home on the farm and up to 4500 sq metres of land, measured as a percentage of the total sale price, will be subject to a capital gains tax.
That will apply even when a farm is inherited by or sold to a family member but may be deferred in some circumstances under the rollover relief provisions.
After the tax report was revealed, Peters was unusually circumspect in what he thought about the report.
For the next two months, Robertson and Ardern will negotiate a package that must have the support of New Zealand First but at the same time creates problems for Labour.
Labour cannot fiercely defend the package it really wants - comprehensive - while in delicate negotiations.
Ardern will remain deliberately muted in her advocacy of a capital gains tax - despite her being passionately in favour of it.
A comprehensive capital gains tax is such a potent political weapon - and so unlikely to be implemented - that Ardern cannot run the risk of being associated with it.
Her captain's call at the last election to allow a CGT to be implemented in the current parliamentary term damaged her campaign and had to be reversed.
Ardern's relative silence presents a huge opportunity over the next two months for National to hammer home the effects on people's lives, not least on small businesses, when it difficult for Labour to defend.
Labour's case will be made by unions, NGOs, economists, and the Greens.
For each graph and statistic wheeled out to support arguments of fairness, National can wheel out hundreds small business owners who have battled their way to success.
The regions are full of them. New Zealand is full of them.
New Zealand First would be dicing with death if it supported a comprehensive CGT on small businesses, including farms.
After the Government's tax plan is revealed in April, and assuming it goes with a diluted CGT, National is relishing the chance to blame any CGT on New Zealand First.
It may not be so simple. If New Zealand First can stop the Labour-Greens this term to have a CGT apply to farms and business, it will have a strong case to argue it would similarly be needed next term.
For as long as the polls have Labour and the Greens with a clear majority over National, New Zealand First may be a more attractive insurance policy against future moves of CGT than National.
What National assumes will be a worse position for Peters and New Zealand First, could in fact put them in a better position to prosecute their relevance in the contest for heartland New Zealand.
But before it does that, however, Peters will needs to brush up on the detail.
