A telephone executive died after being slashed in the neck with a broken beer bottle at an event where singer Jessie J had been performing, jurors have heard.
Phillip Sherriff, 37, had been at the bar of the Pulse nightclub in central London when there was jostling by Ashley Charles, 26, who was trying to get free beer.
After becoming irritated, Charles grabbed a bottle from Mr Sherriff's hand and slashed it into his neck in a second, said Duncan Penny, prosecuting.
He told the Old Bailey: "Eyewitnesses described it as a swipe or slash.
"It happened very, very quickly indeed - perhaps one second, one second to take a life."
Mr Sherriff began to bleed profusely as vital blood vessels had been cut. He died four days later in hospital.
He had travelled to London from Preston, Lancashire, with colleagues for the promotion event in April organised by mobile phone company BlackBerry, where he worked in management.
Charles had travelled to London with his brother and friends from Leicester to attend the event where Jessie J and others performed.
Charles, of Nevanthon Road, Leicester, denies murdering Mr Sherriff.
Mr Penny said the clash came about just after midnight after the performers had left. He alleged Charles became annoyed with Mr Sherriff who was joking about.