The fatal stabbing of a teenager by his friend was an "accident waiting to happen" as they acted out "middle class gangster" fantasies, a court heard.
Yousef Makki, 17, was stabbed to death on 2 March in a row over an attempt to rob a drug dealer, Manchester Crown Court was told.
Boy A, also 17, denies murder, claiming he acted in self-defence after Yousef pulled out a knife.
The barrister defending Boy A said his behaviour was "not sinister - stupid".
In his closing speech to the jury, Alastair Webster QC, said Yousef, Boy A and a second youth, Boy B, had led "double lives".
Despite the privileged backgrounds of the defendants, both from wealthy Cheshire families, they spoke and acted like "middle class gangsters", said Mr Webster.
Calling each other "Bro" and "Fam", the defendants smoked cannabis, listened to rap or drill music and Boy A posted videos on social media posing with his "shanks" or knives, the jury was told.
Mr Webster said social media videos shared by the boys showed "juvenile gangsters playing around with knives" but described their behaviour as "silliness" which showed the stabbing was an "accident waiting to happen".
"They appear to have led double lives, living out idiotic fantasies," he added.
"Talking in stupid jive talk.
"Idiotic, juvenile, pathetic, but not sinister - stupid."
Prosecutors have told the trial Boy B arranged a £45 cannabis deal and the teenagers planned to rob the drug dealer.
When the robbery went wrong Yousef and Boy B fled, leaving Boy A to take a beating, the trial heard.
Boy A has admitted lying to police at the scene and has pleaded guilty to perverting the course of justice and possessing a flick-knife.
He denies murder and a charge of conspiracy to rob.
Boy B, also 17, has admitted possessing a flick knife but denies perverting the course of justice and conspiracy to rob.
The trial continues.