Tony Abbott has broken a week-long media silence to categorically deny that he punched a wall next to a female university political rival in 1977, but admitted to calling her "childish and immature" names.
He also said the allegations were "the product of the Labor Party dirt unit".
The Opposition Leader admitted on breakfast television he referred to former Sydney University student Barbara Ramjan - who beat him in an election for the student representative council presidency - as a "chairthing", after she asked to be called chairperson instead of chairman.
"I probably was guilty of using that silly phrase," he told the Nine network.
"A lot of childish and immature things happen on student councils and I think I probably was guilty of using that silly phrase. Silly things happen on campus."
Responding to claims by former Fairfax journalist David Marr in the latest Quarterly Essay that Mr Abbott had physically intimidated Ms Ramjan by punching a wall either side of her head, the Opposition Leader issued a flat denial.
"I had no recollection of it because it had never happened, simple as that," he told the Nine network. "It never happened."
He also questioned why it had taken Ms Ramjan "35 long years" to bring the alleged incident up.
Mr Abbott initally told Marr he had no recollection of the alleged incident, saying that ''it would be profoundly out of character had it occurred'', but once the story was published over the weekend he denied the event through a spokesman.
Ms Ramjan's account was backed this week by Sydney barrister and former student David Patch, who wrote in Fairfax papers that Ms Ramjan told him about the incident soon after it happened.
"I did not see the incident, but I was nearby," he wrote in Fairfax newspapers.
"[Ms Ramjan] told me that Tony Abbott had come up to her, put his face in her face, and punched the wall on either side of her head. So I am a witness."
Mr Abbott says Mr Patch "didn't see it because it never happened".
The Liberal Party leader brushed off a further claim by an unnamed source in Fairfax papers who said he had witnessed the actual incident. "To remain anonymous does not give an enormous amount of credibility to his or her statement," Mr Abbott said.
He said the allegations were a product of the Labor party "dirt unit" and "a desperate Labor government doing desperate things to win an election they absolutely do not deserve to win".
He pointed out Mr Patch ran as a Labor candidate for the Sydney seat of Wentworth in the 2004 federal election.
The Opposition Leader said he had spoken to his wife and their three daughters to warn them he expected there would be "a lot more of this type of thing in the media before polling day".
Mr Abbott recalled his university rugby playing days and admitted to throwing the odd punch on the field, but said he was more often than not on the receiving end.
"If you go back to the 1970s and the 1980s and you watch footage of Sydney grade rugby matches from those days, there were a few punches thrown and yes, I admit it, I was one of them.
"I think I can safely say that I was hit far more often – I was much more of a punchee than a puncher."