Son in court for assaulting and threatening mother

"You're lucky that's all I'm going to f***ing do," Cody Amer told his mother after slapping her in the face during an argument.

Later, as she fled the house in fear, Amer called out she "better run" because he was going to slit her throat.

Amer, 24, appeared in the Whanganui District Court on Tuesday, where he told Judge Philip Crayton he had sorted things out with his family and they were all "getting along".

At the time of the offending on July 17, he and his girlfriend and child lived with his parents in a rural Whanganui home.

He and his father began arguing about the living arrangements, and when the argument ended, Amer's mother went to the bedroom to pack belongings to leave for the night.

Amer followed her and "reignited the argument", police prosecutor Sergeant Drew Morrison said.

"As he went to walk out, the victim tried to lock the door behind him," Mr Morrison said.

Amer called her a "whore" and a "f***ing slut" and she replied he was a "wanker".

That was when Amer slapped her across her face.

At that point, Amer's father said he was going to call the police, but Amer took the router, which controlled the house's phone line.

The father headed to a neighbour's house to use their phone, while the victim stayed inside and tried to lock all the doors and windows to keep Amer out.

However, he was able to reach through a cat flap to unlock a door, and came into the house, Mr Morrison said.

The victim ran away to a neighbour's house, with Amer calling out from a window: "Yeah, you better run, you c***, I'm going to slit your throat."

When spoken to by police Amer said he had grabbed the victim's glasses off her face.

He pleaded guilty in court on Tuesday to common assault and speaking threateningly.

Judge Philip Crayton referred the matter to Restorative Justice and remanded Amer to October 28 for sentencing.