A knife-wielding teenager warned: “I’ll show you what I’m made of” before masking his face and stabbing a Wolverhampton father-to-be to death in a city pub, a murder trial heard.

Michael Brown, aged 19, was “berserk, ballistic, wild and scary” on the night he killed Andrew Diack at the Flying Dutchman in Merry Hill, it was alleged. Prosecutors say Brown stabbed Mr Diack once through the heart after the victim smashed a bottle over his head.

Wolverhampton Crown Court heard that, along with Mr Diack, witness Margaret Marshall was a guest at a birthday party being held at the pub for Leon Ford on February 6 last year.

As the party was winding down in the early hours of February 7, she told the court yesterday how Brown was “shouting, talking in Jamaican and just being really, really loud”.

Ms Marshall said: “I said: ‘What are you being nasty to us for?’

“He just went berserk. He was swearing at us.

“I was that scared I can’t remember what he was saying.

“Andrew turned around and said words like ‘I have had enough of him’.”

Prosecutors say 29-year-old Mr Diack, of Stafford Road in Fordhouses, then smashed a bottle on Brown’s head.

Ms Marshall said Brown then warned: “If you’ve cut me, I’ll cut you.”

Describing the moments leading up to the killing, Ms Marshall recalled Brown then said: “I’ll show you what I’m made of.”

He then pulled his scarf or polo neck jumper above his nose, leaving only his eyes on show, pulled his cap down and went after Mr Diack.

Brown was said to have chased him into a darkened area of the pub, using his mobile phone light as a torch to seek him out and stab him once through the heart.

The victim tried to escape through a staff toilet window but died.

Brown, of Langley Road, Merry Hill, admits manslaughter but denies murdering Mr Diack, who was a director of a road marking company called STS.

The jury was told he will argue he was provoked or suffering from an abnormality of the mind at the time.

The case continues.