He's labelled him 'Simple Simon', he's described him as a "fool", and he's constantly mocked his accent - but Winston Peters isn't ruling out working with Simon Bridges after the next election.
"In politics it's a fool who says never," he told Newshub political editor Tova O'Brien on Thursday.
"And you never say never, because you don't know what the public tells you... in the end, they are the masters."
- Labour calls for electoral donation reform after Jami-Lee Ross saga
- National Party put me in 'similar situation' to Jami-Lee Ross - Winston Peters
- Jacinda Ardern 'rejects' notion Winston Peters holds the reins
But the Deputy Prime Minister doesn't believe the National Party leader will make it to the next election, saying he doesn't even think he'll be in the job in six months' time.
"I've been in politics for a long time, and I look at people from this point of view: 'Is this person someone whose persona adds to the full picture of his party, grows the image of the party and grows his popularity, or does this person drain the party of its popularity for his or her sake?'" he told O'Brien.
"Sadly for Simon, he's a nice guy, but he's not a contributor in terms of expanding the party's support. He drains it. And that's why he will not be successful."
It's not the first time the New Zealand First leader has taken aim at Mr Bridges' leadership, which has come under scrutiny during the Ross saga and a subsequent investigation into the culture of the National Party.
During a particularly heated Question Time in Parliament this week, Mr Peters used the point of order procedure to say: "Mr Speaker, it's one thing for the leader of the Opposition to be shouting out and protesting during an answer, but all the contenders can't do it as well."
The comment implied that Mr Bridges' role as leader of the National Party was fragile and could soon be up for debate.
Speaker Trevor Mallard then rose to his feet to make Mr Peters apologise for the comment.
"The most experienced Member of the House knows he should not use the point of order procedure to be disorderly himself," he said.
Mr Peters then stood to apologise, but not without his signature grin.