The court heard that on April 2 about 4.45pm, Toon was standing naked on top of the sand dunes at St Kilda Beach.
He was in a clearing in the bushes and was fully visible to people on the beach.
Two 14-year-old girls walking a dog saw Toon doing an indecent act and walked away.
When police arrived about 15 minutes later, he was seen continuing his earlier behaviour.
The defendant told police he knew his actions were wrong, but did not provide any further reason for his behaviour.
On Thursday, counsel Anne Stevens, KC, said her client lacked insight into the offending, but was sorry about it.
"I think it would be fair to say that there is a significant risk of reoffending because of that lack of awareness", Mrs Stevens said.
"The focus must be on protecting the community and Mr Toon from further offending."
She also said her client was haunted by events in his difficult past and struggled developmentally.
Judge David Ruth agreed the community and the defendant needed to be protected.
"You have a concerning history, but perhaps surprisingly, nothing since 2012", the judge said.
"If it were not for your age and particular characteristics, something perhaps more punitive might have appealed to the court."
Judge Ruth sentenced Toon to 18 months’ intensive supervision.
felicity.dear@odt.co.nz , PIJF court reporter
