A then-senator's comments about Greens MP Sarah Hanson-Young sought to imply she was a narrow-minded, one-dimensional misandrist, her defamation hearing has been told.

David Leyonhjelm's comments, including saying she said "all men are rapists", undercut her advocacy for women and children to be safe from violence, Senator Kristina Keneally told the Federal Court in Sydney on Monday.

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She was the first witness at the defamation lawsuit brought by Senator Hanson-Young against the former Liberal Democrat senator over comments he made in three media interviews he gave between June 28 and July 2 2018 and in a media statement.

In the material, he elaborated on his comment to Senator Hanson-Young on the floor of parliament to "stop shagging men" amid a debate on legislation seeking to prevent violence against women.

She says she was defamed by his portrayal of her as a hypocrite and misandrist, in that he alleges she said words in parliament that were "tantamount" to claiming all men are rapists but "nevertheless had sexual relations with them".

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Mr Leyonhjelm contends any reputation damage arose from her own words when she said "he's slut-shaming me" during a radio interview.

Her barrister Kieran Smark SC on Monday told Justice Richard White that his client "steadfastly denied" that she made "the absurd" men-are-rapists statement, submitting it was up to Mr Leyonhjelm to prove his allegation.

"It is not the case that outside parliament it is open to anyone to say anything they like about politicians," he said.

"It is not open season on politicians."

Under cross-examination from Mr Leyonhjelm's barrister, Tony Morris QC, Senator Keneally agreed "slut-shaming" could refer to a person of low sexual morals and someone taking advantage of that, or to painting someone as having low sexual morals.

She said it was not appropriate for a person's sexual activity to be used as a political weapon.

Former trade unionist Bill Kelty said Senator Hanson-Young had been "deeply hurt" by Mr Leyonhjelm's statements.

The 71-year-old agreed that he had suffered "slings and arrows" in his long public life but said no one ever accused him of being against women simply because they are women, or being hypocritical.

Previously he had not known of the "slut-shaming" phrase, but found out it meant Senator Hanson-Young had to justify her private sexual activity.

"Not on one occasion in my entire public life, have people asked me to explain my sexual preference or priorities or sexual relationships - not once," he said.

The hearing is continuing.