A pregnant woman had a knife held two inches from her throat as her mother's partner turned violent in their home.
Preston Crown Court heard David Jones, 34, of Swindon Avenue, Blackpool, told her: "What sort of mum leaves her daughter with a man holding a knife to her throat?"
Her terrified mum had gone outside momentarily to seek help after Jones, who had been drinking, turned abusive.
Preston Crown Court was told his victims were his partner and her daughter, who was 13 weeks pregnant at the time.
The argument is said to have started when he discovered the woman had not named him as next of kin when he went to pick up some medicine for her from her GP's surgery.
Prosecuting, Hanifa Patel said: "The complainant says five month prior to the offence things began to become a little bit sour.
"At around 4.30pm on January 3 the defendant had returned home having been to her GP to collect medicine for her.
"She describes an argument taking place as a result of the fact the defendant was upset the victim had not registered him as next of kin. An incident had taken place at the GPs where they wouldn't disclose information because of this.
"The victims stated the defendant had been drinking for a couple of hours and came upstairs for some tobacco. When he did this he made some nasty comments to the victim and her daughter.
"At around 1am the defendant came back upstairs and was described as being abusive towards her daughter. Because she was pregnant the victim told the defendant to stop."
But when she went downstairs to check on Jones he was making attempts to self harm.
He then locked himself in a bathroom and threatened he would hurt her daughter.
As the incident unfolded and his partner tried to get help from neighbours, he armed himself with Stanley knife and began making stabbing motions, damaging the staircase.
He then pushed his way into the daughter's bedroom and threatened to stab the dog before pointing the knife at the mum-to-be's throat and laughing.
He said: " Come on let's start - you think you're hard."
The terrified mum was trying to get help, and when she returned he said: " It's your turn now" before pushing her into the bathroom.
The court heard he closed the door behind him and sat on the floor, preventing his partner from leaving.
He told her if anyone called the police he would "slash her kneecaps open".
He then began to pull her clothing off and stated he could "rape her if he wanted to".
When an armed response unit arrived, Jones went to a bedroom and and picked up a large sword before running out the house and waving the sword around.
He has since admitted affray.
Jailing him for six months, Recorder Carwyn Cox said: " This was a lengthy incident lasting several hours.
"I take the view the fact that she was pregnant does make her vulnerable."