Rory Amon was a 27-year-old aspiring politician when he met the teenager at his Sydney apartment block in July 2017.
He admits meeting the 13-year-old and having sex with him on one occasion at night in an underground car park bathroom.
However, he claims he thought was the youth was actually 17.
This claim should be rejected, crown prosecutor Meaghan Fleeton told a NSW Supreme Court jury on Tuesday.
"You would not believe his self-serving evidence," she said during closing submissions.
"Using your common sense and experience, you may have very little difficulty finding this accused is guilty."
It would have been obvious to Amon when he met the boy in person that he was under-age, she argued.
She said the intelligent, articulate former MP had lied about his age to manipulate the boy when they first connected on a gay hook-up app.
"The accused Rory Amon instead used a fake name, hid his identity and then deliberately pursued (the alleged victim) and sexually assaulted him."
The alleged victim was a child with no sexual experience at the time, she said.
"This is not some regular user of a gay hook-up site."
The now 36-year-old Amon has pleaded not guilty to 10 child sexual abuse, child rape and indecent assault charges.
He admits meeting the boy once when sexual activity took place, but denies allegations of a second meet-up.
The alleged victim says the ex-MP again came to his apartment, bringing a towel, and that they went down into the car park bathroom where more sexual activity occurred.
"You saw (the complainant) get upset when shown the photos of the car park toilet - that dirty, hidden car park toilet - where he had his first sexual experience," Ms Fleeton told the jury.
"It was a significant and life-changing course of events."
There would have been a window of opportunity in July 2017 for both of these "hasty hook-ups" to have taken place, she argued.
She said the alleged victim's evidence about two meetings should be believed, describing him as honest and sincere.
Being 13, he could not have consented to what happened, but was left with feelings of shame, guilt and embarrassment, she said.
Soon after the alleged sexual abuse, he gave some details of what occurred to his mother, friends, school counsellor and psychologist, she noted.
The complainant first became aware of Amon's identity in 2020 through a COVID-19 announcement when the former Liberal was a councillor.
The two reconnected on Snapchat in 2019 and then on Grindr in 2020 when Amon sent him some photos, including one in his volunteer firefighters uniform.
Five years after the alleged sexual abuse and rape, the complainant first made a formal complaint to police.
The trial continues.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
22°C