An unemployed plasterer has told jurors he killed a young banker after he was "laughed at" and called a "half chap".
Trevor Timon, 31, allegedly punched 30-year-old Oliver Dearlove in the head after becoming angry that he and his friends were talking to a woman he knew.
Mr Dearlove, who lived with his long-term girlfriend in New Eltham, had a brief chat with the woman after spending the evening drinking with old university friends in Blackheath, south-east London.
Timon, from Plumstead, south-east London, has denied murder but admits manslaughter.
Giving evidence, he said he left school at 16 with three GCSEs and got a job as a plasterer.
After four years, he became unable to work because of epilepsy, he said.
On August 27 last year, Timon had met a close female friend and three other women in Morden's nightclub for a birthday celebration.
He bought a bottle of champagne for the women and drank two glasses himself, he said.
Timon said he felt "happy" and not drunk as they left the club together to get a cab home.
He said he walked up to one of the women to "tell her to hurry up because she had her shoes off".
Timon told jurors he asked her "what are you saying?".
One of the young men replied "nothing to you mate", the defendant said.
Then it all "closed in" and an argument erupted, he said.
"We were just standing there having an argument. One of them said 'she's with the half chap'.
"They were laughing at me really, that's the way I took it.
"I said 'what do you find so funny in saying that. Just go away.'
"I did say to one of the guys 'if you don't get out of my face I will knock you out'. It's a figure of speech really."
One of the women was urging them to go but the shouting continued, he said.
Defending, Courtenay Griffiths QC asked: "Who was the first person to do anything physical?"
Timon replied: "Me. I punched him. He fell backwards. He just fell.
"I stood there for a couple of seconds and walked off."
Asked what was going through his mind when he threw the punch, Timon said: "Nothing. I just threw a punch. I don't know."
Mr Griffiths said: "What were you hoping to achieve?"
The defendant replied: "Nothing. I was pissed off."
He continued: "I was shocked. I didn't think it was that serious. When I got the phone call (from one of the women) to say he was in hospital I was shocked to hear that. I could not believe my punch had led to hospital."
Timon said he went to London City Airport and got on a flight to see his mother in Ireland.
After a couple of days, Timon said he returned and went straight to a police station with his father.