Jimmy's older brother, Harry Mizen, had a history with the accused
A man accused of murdering 16-year-old Jimmy Mizen admitted that he threw a glass dish at the schoolboy, but said he did not intend harm.
Jake Fahri, 19, from Lee, south-east London, denies murder after the dish severed an artery in Jimmy's neck, causing him to bleed to death.
Mr Fahri demonstrated in court how he threw the oven-proof dish after the two began fighting over a sign in a bakery.
The attack happened in May 2008 at the Three Cooks Bakery in Lee.
Giving evidence at his Old Bailey trial, Mr Fahri said the pair were arguing when he grabbed an advertising sign, leading to a "tug-of-war".
Mr Fahri told the court he felt Jimmy would take it off him and he looked around for something else.
He said: "I grabbed the dish by its side. I threw it forward in front of me. I knew Jimmy was in front of me and I threw it in front of me.
"I just wanted him to let go of the sign. I thought he might put his hands up. I didn't think it would hit him. I just flung it."
Mr Fahri said the incident had taken two seconds.
He added: "I saw it hit his face round the jaw area. I saw the glass broke and I saw a bit of red.
"I was shocked. I could not believe what happened.
"I saw it cut him - that was the last thing I thought would happen. I was scared. I just ran.
"I didn't think I fatally wounded him. I cut him, I cut his face."
'Impotent with rage'
Mr Fahri also said he felt "horrible" about Jimmy's death.
"I should have just walked away. Maybe it was a bit of pride.
"I have a mum and dad. He has a family and I feel horrible. I didn't mean to do it."
Mr Fahri said he threw the glass plate in self-defence and denied the prosecution's allegation he was "impotent with rage".
The court earlier heard Mr Fahri had hit Jimmy's older brother, Harry Mizen, when he was at school in 2003, after his mother complained to the school about Mr Fahri bothering her son.
The trial also heard that a shard of glass from the dish had shot 1.6in (4cm) into Jimmy's throat and the impact was such that pieces of glass were found 6ft (1.8m) above the ground.
The trial continues.