A Sydney labourer, who unleashed a torrent of explicit abuse online after a screen shot of a woman's Tinder profile was uploaded to Facebook, told police he was drunk and unaware that trolling was a crime, court documents show.

Zane Alchin​, 25, from Caringbah in Sydney's south, has dropped his fight against one count of using a carriage service to menace, harass or offend. His lawyer, Pierre de Dassel, entered a plea of guilty on his behalf in the Downing Centre Local Court on Monday.

The offence occurred after another man posted a picture of Sydney woman Olivia Melville's profile on dating application Tinder to his Facebook page in August 2015.

He has not been charged with any offence.

Ms Melville's Tinder profile included a picture of her and Canadian hip hop artist Drake's lyrics "Type of girl who will suck you dry and then eat some lunch with you".

Ms Melville uploaded a screen shot of the abuse she received to her own Facebook page and friends left supportive messages.

Alchin then posted 55 comments, many obscene, over a two-hour period, including a reference to the "best thing about raping feminists".

"I think you should have ya tubes tied baby," he posted at one point.

"What law am I breaking? I'm not the one out of the f---ing kitchen," was another.

Fairfax Media has chosen not to publish other, more explicit, messages.

Paloma Brierley Newton, 24, took screen shots of the abuse that was directed at her and others and handed them to police, but said officers initially offered little support.

Several woman, including Ms Brierley Newton, created a Facebook group "Sexual Violence Won't be Silenced" and launched a petition for tighter laws and more resources to tackle online harassment, both of which attracted thousands of supporters.

Court documents show that, when Alchin was arrested in October, he told police of one explicit post that he wrote: "I got it off an anti-feminist website. To offend a group of feminists that were harassing me and my friends."

While Alchin admitted to posting the comments, he told police during an interview that "he was drunk at the time and the comments do not represent what he is about", the court documents said.

He said he was internet trolling and was unaware it was a crime, the documents said.

In January, Alchin entered a plea of not guilty to the offence, which carries a maximum penalty of three years' imprisonment.

But during a brief court appearance on Monday, his lawyer said his client would now plead guilty. Alchin is due to be sentenced on July 29.

Outside court, Ms Brierley-Newton said she hoped the case set a precedent and showed that no one should have to put up with harassment or bullying online.

"I think that, by standing up and saying that he is guilty of a crime, it can put an end to all the backlash of, 'This is just the internet, this isn't a crime,' " she said.

Alchin covered his face with a suit jacket as he left the court, while a man accompanying him told reporters and photographers: "This is harassment."