The offensive behaviour of Maurice Williamson highlights a problem in the National Party with how it treats such behaviour towards women and minorities, the Labour Party says.
Susan Jones, an Auckland IT consultant who was at the event, said she was gobsmacked by Mr Williamson's presentation and described it as shockingly crude pub talk.
She said it included sexual references, images of scantily clad women and a sexually explicit audio advertisement with homophobic references.
She said many people were groaning and some even walked out of the event.
In a statement Mr Williamson said he was asked to be as entertaining and funny as possible, but overstepped the line, causing offence for which he unreservedly apologised.
Prime Minister John Key said Mr Williamson clearly regretted his behaviour and said hopefully it would not happen again.
He said Mr Williamson did not attend last week's event in his capacity as an MP.
But Labour women's affairs spokesperson Sue Moroney said that did not wash.
"Look as Members of Parliament we're always there in our capacities as MPs, we are public figures - that's what we do.
"I think it's a pretty poor excuse from the Prime Minister who is obviously feeling pretty compromised about the way he dismissed his own ponytail pulling habits - I think that has really compromised his ability to deal with this issue with one of his own MPs."
Green Party co-leader Metiria Turei said Mr Williamson was obviously invited because he was an MP.
"He did a terrible job of [hosting the event], people walked out and were deeply offended.
"New Zealand women deserve much better from our Prime Minister and his MPs than this kind of sexist and derogatory behaviour."
Ms Moroney said the incident was indicative of a deeper problem in National.
"I think this is now just more evidence of some issues within the National Party around how they treat offensive behaviour towards women and others, and the Prime Minister really needs to take hold of this and address it."
Ms Moroney said John Key should publicly reprimand Mr Williamson to send a stronger message that such behaviour was unacceptable.
It was not the first time Mr Williamson's mouth had got him in hot water.
He resigned as a Minister last year after he contacted police on behalf of a businessman facing domestic violence charges.
And he was also in the headlines in 2010 for telling insulting jokes about Muslims and Pacific Islanders at another event.