Be careful says man whose tweets cost

Be careful what you tweet.

That's the message from a NSW man ordered by the District Court to pay $105,000 for defaming a teacher at his former high school on Twitter.

Andrew Farley said he only had about 65 Twitter followers and 50 Facebook friends when he made comments about Orange High School music teacher Christine Mickle in 2012.

Mr Farley, who graduated from the school in NSW's central west in 2011, is the son of the school's former music teacher who reportedly left the position due to poor health.

He said the comments, posted on Facebook and Twitter, "were never meant for public broadcast".

"It was a discussion between four of my friends," he told Newcastle radio station KOFM on Thursday.

"I had no idea that anything I wrote as a teenager ... would ever get such a huge and devastating effect on the teacher."

Mr Farley's case is believed to be the first Twitter defamation case to go to full trial in Australia.

A judge ordered Mr Farley to pay $85,000 in compensatory damages and an extra $20,000 in aggravated damages.

Mr Farley says the comments about Ms Mickle were a one-off.

"This has really shaken me," he said.

"I have been depressed, I have been seeking help for my mental state.

"It's all because of one comment on Facebook (and Twitter)."