Labour leader Jacinda Ardern says if her mother caught her swearing like ACT Leader David Seymour, she would probably "get a talking to".
Mr Seymour was speaking at a Business NZ conference when he called New Zealand First MP Richard Prosser a "f**king idiot".
Mr Prosser had earlier told the conference at Te Papa that his party would bring electricity assets back under a state-owned, state-controlled umbrella.
"That means if you have shares in Contact - get rid of them now," Mr Prosser said.
Asked how he proposed to fund an $11 billion buy-back of electricity companies, Mr Prosser said they would be bought back over time at the price they were sold for.
Mr Seymour told the audience that statement showed how the last nine years of having reliable, orthodox economic policy could crash down in four weeks' time.
"The idea that you would have somebody who pretends to hold the balance of power - to come and tell you that a stock trading at $5.85 is going to be nationalised at $3.10 and you better all sell it.
"Well, I realise that in a role such as mine you are supposed to have a certain amount of decorum ... but that makes me really angry - what a f***ing idiot," Mr Seymour said to laughter and applause.
Ms Ardern, speaking to media today, said "if my mother caught me swearing in the way that David Seymour did, I'm sure that I would get a bit of a talking to".
"One of the reasons that some of our voters have disengaged, particularly our younger voters, is that they don't want to see combative politics."