A guest at a country house party appeared to be proud of his actions just moments after he stabbed his young nephew to death with a wine glass.
Raymond Dupree, aged 68, stood over seriously injured victim Ryan King and said "You're down now" and boasted "I've done him", a jury has been told.
Ryan, aged 20, died from loss of blood after the fluted white wine glass shattered as it was slashed across his throat and severed the jugular vein.
He was one of 30 guests at his mother Lisa Wilson's 40th birthday party at his grandmother Bernadette Soton's country mansion at South Molton 13 months ago.
The jury at Exeter Crown Court were given a graphic demonstration of the attack by another guest and were shown the bloodied wine glass which was found on a kitchen chair.
Former boxer Dupree, of Bishops Nympton, near South Molton, denies murdering Ryan King at the party at Snurridge House in August 2011. He says it was an accident.
Guest Sarah Campbell, who is a close friend of Ryan's mother, said she had stopped drinking and was clearing up when the trouble started.
Dupree became angry when one 14-year-old girl accidentally dropped two glasses onto the kitchen floor and then ordered another to stop the music and go to bed.
She sobbed as she said: "He was getting quite uptight and he referred to one of the girls as a gobby cow. I said they were only kids. They were giggly and playing a bit of music and singing and messing around.
"He went over to one of the girls and said she should be in bed. He ordered her to go to bed in a stern manner. She said no.
"Two of the girls moved around the dining room table to get away from him. Ryan said to him to leave it out and said they were only kids and he should leave them alone.
"Dupree started pointing at Ryan and jabbing his finger and said he should respect his elders. I took Ray's arm to calm him down but he knocked me out of the way.
"Ryan stepped forward and asked Ray if he was picking on his own family now. He had his hands up in a gesture of submission and was not aggressive at all and was calming the situation down.
"They moved into the kitchen and I was not paying attention when I heard a slapping noise and saw Ryan with people around him. He had been knocked back and was sat on the floor holding the left side of his face and neck.
"Dupree was stood over him and what he said surprised me and shocked me. He said something like 'you're down now'.
"I thought it was not nice. He said it like he was proud that he had done it. He may have said something like 'I've done him'.
"Ryan was helped to a chair and as he sat down he took his hand from his neck and looked at me and said 'I'm going to die'."
Fellow guest Adam Thorne, who was stood just feet away, gave the jury a demonstration of how Dupree picked up a glass from the kitchen table and swung through 180 degrees before making contact with Ryan.
He told the jury the attack was unprovoked. He said: "Ryan had not done anything to suggest he was going to attack Raymond. Ryan was totally non aggressive but Dupree was angry."
Members of Ryan's family wept as the court was played the recording of Mr Thorne's call to the emergency services in which he relayed advice to fellow guests on how to treat the injured man.
The trial continues.