Wonder French had sex with Ryan Jones, 24, after getting on a bus at Charlestown at 9.50am on March 29.

The 31-year-old has pleaded guilty to offensive behaviour, inciting the commission of crimes and using offensive language after initially denying the charges.

Belmont Local Court magistrate Peter Barnett told French her conduct had been unacceptable.

"Quite frankly, I can't think of a worse example of offensive behaviour,'' Mr Barnett said on Wednesday.

"Your conduct on that day was absolutely extraordinary."

Mr Barnett told the court he ordered a sentencing assessment report for French, but she had failed to contact Corrective Services.

The magistrate told French he understood she was homeless, suffering mental health issues, had been using ice and had on-going domestic violence issues, but the report had to be completed before sentencing.

French was ordered to appear on Thursday in Newcastle Local Court, where Mr Barnett planned to set down a sentencing date in late November so the report could be finalised.

Jones, who suffers from schizophrenia and anti-social behaviour disorder, had six charges including behaving in an offensive manner withdrawn under the Mental Health Act.

In a police statement of facts, bus driver Hugh Williams told how he looked in his rear view mirror and saw Jones and French engaging in sexual activities on the back seat.

When the bus driver stopped to pick up a female passenger at Warners Bay, he decided to order the pair off the bus "as their sexual behaviour was offensive to others".

Jones, unemployed and homeless, replied: "Don't kick us off. We gotta get to the Toronto Drug Court."

Police said French was inciting Jones to be abusive and violent, yelling: "Tell him to get f***ed. It's not his f***ing bus. Tell him to f*** off."

The bus driver became concerned and activated the duress alarm before Jones told him, "I'm gunna get locked up if I don't get to court, you f***ing dog" and spat on him.

When the pair tried to get on a second bus and were told they were not welcome, French abused the driver, Brett Teasdale, telling him: "Do what you're f***ing told c***. It's public transport, so you have to f***ing take us."

French then incited Jones to be more abusive and violent by telling him: "You're going to be locked up anyway babe. Just do it."

Jones then told Mr Teasdale, "I'll f***ing smash you c***. I'll come up there and smash you" before the driver decided to remove all the passengers from the bus.

Australian Associated Press