Mark Latham's lawyer admits a tweet that prompted independent Sydney MP Alex Greenwich to sue the ex-One Nation NSW leader was vulgar, shocking and caused almost universal revulsion, but has argued it wasn't defamatory.

The post was published in the aftermath of a rally last March when LGBT protesters were targeted with violence outside a Sydney church Mr Latham was scheduled to speak at, just before the state election.

It was a response to comments Mr Greenwich made in a news article about the church incident, including a description of Mr Latham as "a disgusting human being".

Mr Latham's tweet began with: "Disgusting? How does that compare with…"

He then referred to sexual activity in words described as "revolting" by Mr Greenwich's counsel in court. The ABC has chosen not to republish the full post.

Mr Greenwich, who has been an openly gay MP for more than a decade, previously described it as highly offensive and homophobic.

Tweet 'didn't wound' Mr Greenwich's reputation, lawyer tells court

The tweet was a "striking publication", Mr Latham's counsel Kieran Smark SC today told the Federal Court in Sydney.

"What we say globally is that Mr Latham's tweet may have wounded Mr Greenwich, but it didn't wound his reputation," he said.

Mr Latham has argued he was publicly attacked before posting the tweet and raised defences of qualified privilege, public interest and honest opinion.

There is also a dispute about whether the case has met a legal threshold of serious harm.

"Those words are vulgar and shocking," Mr Smark said.

Mr Greenwich claims there were four defamatory meanings conveyed by both the tweet and Mr Latham's subsequent comments provided to The Daily Telegraph.

He alleges he was portrayed as someone who "engages in disgusting sexual activities" and "is not a fit and proper person to be a member of the NSW parliament because he engages in disgusting sexual activities".

He further alleges the Daily Telegraph comments implied he "is a disgusting human being who goes to schools to groom children to become homosexual".

In laying out legal principles relevant to the case, Mr Smark said the court must decide whether the imputations were conveyed, whether they were defamatory and whether there existed serious harm.

Mr Greenwich denies his comments were 'provocative'

A second set of issues, Mr Smark said, concerns whether his client can rely on the defences.

Mr Smark said the degree of offence and reaction to the tweet's vulgarity had nothing to do with its allegedly defamatory character.

Mr Greenwich yesterday told the court he had never experienced anything like the tweet in his life.

He denied, under cross-examination, that his initial comments about Mr Latham were "provocative".

The court heard Mr Greenwich was subjected to death threats and hate mail from members of the public, experienced panic attacks and a reluctance to attend large events, and was questioning whether he should continue with public life.

The hearing, before Justice David O'Callaghan, was initially scheduled to run into next week but is expected to conclude today.