Joe Dinsdale died just over a fortnight before his 18th birthday
A man boasted that his friends could call him a murderer after he stabbed a teenager in the heart in revenge for an argument at a party, a court has heard.
Lewis Gray, 21, of Marfleet Lane, Hull, denies murdering 17-year-old Joe Dinsdale in February.
Hull Crown Court heard Joe died from a single stab wound to the heart after being attacked in the street.
In police interviews Mr Gray said he stabbed Joe by accident, but witnesses said he "appeared proud" of the attack.
The jury was told that Mr Gray was angry with Joe after the two men had an argument at his flat.
Bryan Cox QC, prosecuting, said the details of the argument were not clear.
After Joe had left the flat, Mr Gray went to the house of a friend's father where he armed himself with a knife before shouting to Joe, "Come on then", the jury heard.
Witnesses described how Mr Gray then produced the knife from behind his back and stabbed Joe in the chest.
Mr Cox told the jury that, according to witnesses, Mr Gray then boasted about the attack.
He said: "Immediately after the stabbing, he held the knife up and remarked that there was blood on it and he appeared proud of himself and had a smile on his face.
"According to two of the girls present in the group, the defendant said, 'Now you can call this man a murderer'."
The knife was later recovered on the roof of a primary school where Mr Gray told police he had thrown it after the stabbing.
In interviews with police, Mr Gray initially denied any involvement in the attack but later said he had stabbed Joe by accident.
Mr Cox said: "You can be satisfied that the fatal injury inflicted by the defendant was no accident as the defendant was later to claim.
"The defendant had armed himself with this knife to get his revenge for whatever had gone on earlier."
He continued: "The police say that the claim that Joe Dinsdale had a knife was untrue. It's an invention to justify the defendant's use of a knife."
The case continues.