Where the hell do you come up with his not taking responsibility? His saying it was a stupid, impulsive prank is not ditching responsibilty, it's calling it like it was. A dumb thing to do.
I must have hit close to home by your violent reaction.
Shoving a gun in someone's face isn't a prank. Armed robbery is still classified as a capital offense in some states (although the liberal Supreme Court has temporarily blocked the use of the death penalty for the crime.) So what you consider a "prank" could have netted him a life sentence in more civilized parts of the country.
Impulsive? I think he is lying about that as well. Stealing a bicycle leaning against a tree might be impulsive. Armed robbery takes some advanced thought.
"Bent on mischief" - translates to 'not his first criminal act'.
The not so young punk is sill trying to make excuses for his criminal acts an minimizing crimes which could have ended in death rather than facing up to responsibility for his acts.