At Exeter Crown Court on the second day of the Michael Honeysett trial, Susan Kudliskis said he held the handgun only a foot from her face.
'At one stage I thought he was going to pull the trigger,' she said.
She said she thought the gun was real, although when it was examined it turned out to be it an imitation weapon capable of firing metal pellets.
The incident allegedly happened in January after Honeysett married Zelma Kay, the sister of Mrs Kudliskis' husband.
Mrs Kudliskis told the court that before the wedding she had never met Honeysett.
She said that prior to the wedding when she had telephoned Zelma's house Honeysett had answered the phone and he had told her that he was a cabinet maker from Paignton.
'He said he was Michael, he was 5ft nothing and he could beat the s*** out of anyone.
'That was the way he introduced himself. I was quite alarmed,' she said.
During the wedding reception at Honeysett's home in Ayres Close, Bideford, he had produced and opened a flick knife.
"I said I thought the knife was illegal. He said it was his tool, and showed off with it, then threw it to me,' said Mrs Kudliskis.
Later, she said, Honeysett told her: 'You and me need to have a chat,' and they went upstairs to a bedroom.
'All of a sudden he got this gun and was pointing it at me. I did not see where it came from,' said Mrs Kudliskis, adding that the weapon was about a foot from her face.
'As he held the gun towards me, he said "you do not want me as an enemy",' she told the court.
'I did not think what was happening was real. I pushed his arm away, but he put the gun in my face again," she said.
'I thought he was going to pull the trigger at one stage,' she said, adding that she thought the gun was real.
'I was very frightened,' said Mrs Kudliskis.
Honeysett told her he was upset about the way she had spoken to him on the telephone, then got out the knife and threw it on to the bed.
She said he told her: 'You know what a knife can do.'
Mrs Kudliskis and her husband left the reception soon afterwards and called the police.
Honeysett was arrested the following morning but said in interview that he had never threatened her.
Fifty-one-year-old Honeysett has pleaded not guilty to possessing an imitation firearm with intent to cause fear of violence and has also denied a second charge of affray.
The trial continues.