Bankrupt Priory Hall developer Tom McFeely threatened to slit a woman's throat and "send her to America in a box", a court was told.
Mr McFeely (68) is also alleged to have demanded that she hand back money he claimed she owed him.
The woman said she is so afraid of Mr McFeely that she hid in a neighbour's garden to avoid him.
She said he is a "very angry man" and believed he needed help to deal with anger management issues.
The accused, who lives in London, appeared before Tall-aght District Court charged with two counts of breaching a protection order at a house in south Dublin on February 12 and February 20 last year.
Mr McFeely, who has denied the charges, has claimed he did not know a protection order was in place at the time of the alleged breaches.
In her evidence, the woman, who cannot be identified by order of the judge, alleged that Mr McFeely came to her home at 9am on February 12, 2016.
She claimed he was very angry and said he wanted to talk.
The woman alleged that Mr McFeely made a number of threats towards her, saying he would slit her throat and "send her to America in a box".
She also claimed that he demanded back money which he said she had stolen from him.
The woman further claimed that in a second incident on February 20, Mr McFeely said, in a text message: "If you want to be a scumbag there'll be consequences."
She said he also called at her home that day, but she was out. When she returned, she saw him at her front door and hid in a neighbour's garden until he drove away.
The woman, who became tearful while giving evidence, told the court she was terrified of Mr McFeely and in fear of him.
"He's lost everything," she said. "He's had a very bad run of things."
She further claimed Mr McFeely has anger management issues.
Cross-examined by Stephen Montgomery, the woman denied that the alleged argument on February 12 - which she said lasted two hours - was primarily about money or that she could have left the house at any time.
In any case, the court heard that Mr McFeely will deny he was in the woman's house.
Mr Montgomery applied for the case to be struck out, arguing that Mr McFeely did not know a protection order was in place at the time of the incidents.
The court heard the protection order was granted in November 2016 and extended.
Mr McFeely told the court that he did not know about the extension to the protection order.
Refusing the application, Judge John Lindsay said he was satisfied he knew the order was in place.
Mr McFeely told the court that the woman did not need protecting from him.
He claimed her new friends have "gotten their claws into her", are putting ideas into her head and "she wasn't like this two years ago".
The woman denied this, saying this was her decision.
The judge adjourned the case to a date later this month.
Mr McFeely is expected to give evidence when the case returns to court.
Judge Lindsay reminded Mr McFeely that he must abide by his bail conditions, which include signing on three times a week at Letterkenny Garda Station in Co Donegal.
"If you want me to go to jail, I will," said Mr McFeely. "I think everyone would be happy if I go to jail."
The judge warned McFeely to "behave yourself".