When 38-year-old Simon Grant Taylor was asked what he would have done differently, he said: ''I should've pushed the bitch away.''
Judge Michael Crosbie convicted the man of sexual violation by unlawful sexual connection and jailed him for three years nine months.
Taylor will serve the whole term without chance of parole because it was his second strike under the three strikes regime.
He groped another teen in a shop in 2014 and, before the legislation was introduced, was sentenced to five years in prison in 2009 for sex offences against a child.
Counsel Anne Stevens QC said her client led an isolated existence.
''He spends all his days, it appears, on the internet. A lot of it looking at pornography,'' she said.
Taylor had never met the 13-year-old before the evening of May 1 and a police summary stated she came up to him at central Dunedin's bus hub in an agitated state.
''The victim was grossly intoxicated, running and screaming up and down the street without shoes on,'' court documents said.
''She was carrying a container of alcohol, shouting at and confronting members of the public, stumbling and unsteady on her feet.''
When the victim sat down next to Taylor she began touching his crotch over his clothing.
It progressed to hugging and kissing ''within seconds'', the court heard, before she led him to the back of a commercial building in Great King St.
Taylor allowed the victim to perform a sex act on him before they returned to the bus hub. Once there, the girl told him she was a runaway and needed to hide from police.
The pair boarded a bus, bound for Taylor's Green Island home but the defendant's father immediately turned them out.
The victim went back to town on the bus alone and spoke to police that night.
When questioned, Taylor said the girl was ''incoherent'' at times, due to her level of intoxication and claimed she had told him she was 15, 16 and 17 years old.
Taylor said he ''went along with the sexual act anyway, as he was grateful to receive it''.
In August 2014, the defendant was convicted of indecent assault and locked up for six months.
On that occasion he was at The Warehouse in South Dunedin, where he grabbed an 18-year-old woman's buttock in the store's music section.
Taylor explained he found it hard not to touch girls and young women to whom he was attracted.
A psychological report assessed him as a high risk of further sexual offending.
The court heard Taylor had a normal childhood until his behaviour deteriorated at high school and he turned to cannabis and alcohol use.
The defendant was of low intelligence but Judge Crosbie said his mental health issues were not as acute as many who came before the court.
''You took advantage of the situation when you should've distanced yourself from her,'' he said.
