Australian school mums sue each other over "defamatory" WeChat comments.

A squabble between two mums at Knox Grammar has escalated to a Supreme Court battle after the women sued each other for defamation over a series of messages.

Ava Wei Wu and Michelle Li Chen’s friendship descended into an exchange of insults all captured on instant messaging service WeChat, Sydney Morning Herald reports.

After six years of friendship, the fight started when Ms Wu allegedly called her former friend a “green tea prostitute” in a chat forum for Knox Grammar parents one evening in March 2016.

“You really think you are a high-class lady by sending your children to a private school and buying a few fake handbags?” Ms Wu had allegedly posted.

“You are two-faced and ghost-like … And don’t forget the reason why your son got into Knox is because I noticed the vacancy and told you and acted as your referee.”

Not about to let herself be insulted, Ms Chen then took to a different group of more than 1000 WeChat friends to hit back. She allegedly defamed her friend by claiming she nearly killed a policeman by accelerating when he stopped her for a roadside breath test and that she told Ms Chen’s daughter to hit back if she’s attacked, the newspaper reports.

“This is the first time in my life I have met this type of shrew,” Ms Chen allegedly said.

“I feel very sorry to have met someone shitty like you. It feels like stepping on [dog poo emoticon].”

In this case, it was what was implied - the imputation of what was said - that is the problem in these women's messages.

Ms Wu alleges this is defamatory because it claims she "taught children to act with violence" and "attempted to commit the act of murder".

Meanwhile, Ms Chen claims that Wu's words were defamatory because they implied she was disloyal to friends and was a  "savage person likely to cause harm to others".

The fact that you can sue someone over what is said in a group chat may surprise some social media users, but a lawyer told Mamamia that if you write something online - or even send a text message to someone about another person - that counts as "publication" for the purpose of defamation law.

Defamation law doesn't discriminate on where the defamatory words were published. So whether a Tweet or re-Tweet, a rude customer review or a Facebook post - everyone needs to carefully consider what they are saying about others online.

Sydney Morning Herald reports each woman denies the allegations and is using the defence of truth to attempt to quash the suit against them.

It's up to the court to now determine if any of the women's claims are true and if any damages should be paid.

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