He was left without a conviction after he pleaded guilty to a charge of criminal damage when he appeared in Dublin District Court.
Donnan, of Greenfort Crescent, Clondalkin, admitted damaging the barrier at The Square car park.
The investigating garda told the court he was on duty on July 27 when he received a report of a road-rage incident between a black Skoda Octavia and a white van at The Square. He was told the barriers had been broken.
A short time later, Donnan, the driver of the Octavia, came to Tallaght Garda Station and admitted causing the damage.
The court heard he had 22 previous convictions related to "boy racing" but none for criminal damage.
Donnan had been apologetic for what he had done when he turned up at the station, his barrister said.
"He turned up at the station of his own volition and explained what had happened," he said.
"On the night in question, he was rear-ended by another vehicle, he went to pursue this vehicle and in the process damaged the barrier."
The court heard the defendant was living at home with his family and was on job seekers' allowance. He had compensation in court for the damage that was caused.
Judge Catherine Staines applied the Probation Act.