A teenager will spend Christmas in custody after being locked up for groping two girls on separate occasions.
William Dowsett had denied two offences of sexual assault but was convicted by a jury.
Judge Jeremy Carey told the 19-year-old that if he had been sentencing him purely in his interests he would have let him walk free.
“I have no doubt you are now leading a law-abiding and responsible life,” he said.
“You are having a relationship with someone who trusts you.
“You have good prospects work-wise and a supporting family.”
But the judge said it was only one side of the picture.
The other side was he had to be punished to reinforce the message that those who committed sexual offences would go to prison.
Prosecutor Allister Walker said Dowsett picked up one of the girls from Strood station after she and her friend had problems catching a train.
They went to Rochester High Street, where there was a festival, and he grabbed her bottom.
Later, he told her he needed “a sex marathon”.
The teenager then put his hands inside the girl’s leggings and made her touch his private parts.
The girl complained soon after the incident happened, but he was not charged.
The case was reopened when a second similar complaint was made.
Judge Carey said branded the offences “predatory sexual behaviour” against the will of both victims.
Sentencing Dowsett, of Hinde Close, Sittingbourne, to 18 months’ youth custody, he added: “This was serious sexual offences and you must now take the consequences.”
Dowsett’s name will appear on the sex offenders’ register for 10 years.
He will be barred from working with children under 16 or vulnerable adults.