The 19 year old, who can only be identified as Joel for legal reasons, died at the Goulburn Correctional Centre in the southern tablelands of NSW in July 2022.
Joel was charged with robbery while armed with a dangerous weapon in May 2022.
He asked to speak to a psychologist to help him cope with the anxiety of being in jail for the first time the day after the charge.
By July 2022, he gave a note to a prison officer asking him to be moved out of his shared cell.
He feared his cellmate would become aware he implicated alleged co-offenders in his statements to police, the note read.
"I'm scared for my safety having my brief hidden," his note said, according to the officer.
"I don't want anyone to know I'm a dog. Can you remove me please, without my celly knowing?"
Prison officers moved him to a sole cell while his application to be placed in protection was processed.
However, officers "clocked-off" and didn't process the application, the coroner found.
By the next morning Joel was found dead by suicide inside his cell.
His body was discovered after he had been unchecked and unfed for 17 hours.
His last check-in by an officer happened at 2.35pm when he was given dinner.
Prison governor Leah Nicholson said staff shortage and a lack of funding meant that cell observations could only be carried out to those most at risk.
But coroner Joan Baptie said officers didn't do enough to address Joel's concerns.
"It is quite extraordinary that inmates are provided with their dinner at around 2pm, with no additional food being provided until breakfast at 7am, some 17 hours later," the coroner said.
"Inmates are deprived of their liberty, however, should not be exposed to unnecessary hardship and deprivation, including the timeliness of the provision of food."
The coroner probed the application process after Ms Nicholson said it would only take an hour to an hour-and-a-half to process it.
However, Ms Baptie said it is unknown whether his placement in the protection wing would have positively impacted his low mood and concerns.
If the application was to follow the usual timeframe, Joel could have been transferred to the protection wing before he died, she said.
But there was "confusion" on who would deal with the application.
The coroner also criticised how the prison overlooked possibilities that could have facilitated self-harm.
She made recommendations asking Corrective Services NSW to provide training to frontline officers and review its policies.
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