Andrew Clark, 43, was hit with an open palm by Demeish Williams, 30, outside the supermarket on Upper Elmers End Road in Beckenham at around 8.30pm on March 16.
Williams, described as a large and well-built man, had become aggressive after Andrew told him he couldn’t cut in front of them in the queue.
After a brief argument Williams did pay first, but then waited for Andrew outside the shop with a facemask on.
He hit Andrew once to the side of the head before shouting “I told you to f***ing apologise”.
“Mr Clarke did not try to break his fall or do anything. He was just knocked out,” prosecutor Alistair Richardson said.
Andrew sustained critical head injuries and died in hospital three days later.
Williams will be sentenced for Andrew’s manslaughter at Woolwich Crown Court on Friday afternoon, December 12.
A statement written by his daughter was read out court.
She wrote: “I was 13-years-old when my dad was violently killed and I had to spend my 14th birthday without him.
“My dad wasn’t just my dad, he was my best friend. He called me boss, because he said he would do anything for me.
“Our bond was unbreakable from the first moment he held me. We did everything together.”
She asked Williams: “Why did you have to do this to my dad? Why haven’t you shown any remorse. No apology. No explanation. Just silence.”
She told Williams her dad believed in fairness and that’s all he was standing up for that day.
“You get to keep your family whilst you destroyed mine in the most brutal way,” she said.
Andrew was described as a “brilliant dad” and “the man who held their family together”.
He was a massive Newcastle fan and had watched his club win the Carabao Cup final on TV that day.
He described it as one of the best days of his life but an hour later he was fatally attacked, the court heard.
Andrew’s wife told his killer: “You took him us that moment you chose to walk back from the car and inflict the violence that ended his life. Why did you come back? Why didn’t walk away?
“I will never understand why you came back that day. It was deathly dark and you left a small child in that car. When you went back to the car you didn’t leave. You didn’t check on the child. You put on a face covering and came back.
“What type of man choses to kill rather than simply walking away? The type of man who is not a man but a monster.
“You killed Andrew then cowardly ran away. You are a coward. You are a killer. You are a monster.”
She said darkness is now her constant reality.
“I do not want this life. This is the life you forced me to have. I do not want to live without my husband. My daughter does not want to live without her dad,” she said.
She described as “joy, warmth and life”. She said he was a generous man who had never had a fight in his life.
She told Williams: “A monster destroyed my family. A monster killed my Andrew. That monster was you.
“You will not receive a life sentence today but I have one. I will live with grief, trauma and loss for the rest of my life.”
She said the Crown Prosecution Service decision to accept a manslaughter plea left their family with “no sense of justice”.
Andrew’s sister said: “Andrew was not only my brother but my strongest ally and greatest friend.”
She described him as a hero and inspiration to his two nephews and his own daughter.
“He achieved so much in his 43 years of living and we as a family have been so incredibly proud of him. He supported his wife and daughter and always protected them,” she said.
“His wife was with him when he was attacked. It could only be described as demonic that a random man attacked Andrew at all, let alone her have to witness it.”
When Williams was arrested at his home on Fir Tree Gardens in Croydon, his mum said “I know what happened. He told me. The man called him c**t.”
