A young driver resisted arrest after a routine garda stop for "excessive tooting" of his horn developed into a violent roadside row that got "out of control".
Thomas McKenna (20) "got in the middle" of an "outrageous level of resistance" that was put up by his sister when she came over and aggressively challenged gardai.
He was found guilty of obstruction, but Judge Gerard Jones told him he could avoid conviction if he made a €300 charity donation.
His mother, Sharon O'Donnell (43), was charged with the same offence for allegedly getting involved too, but her case was dismissed after Blan- chardstown District Court heard she had been trying to "protect her children".
McKenna and his mother, of St Margaret's Road, Finglas, had both pleaded not guilty.
His sister, Amy McKenna, had previously admitted charges arising from the incident and was not before the court.
Gda Sinead Tyrell said she was driving with Gda Hayley Robinson on Cardiffsbridge Road, Finglas, at 10.43pm on September 21, 2017 when she passed a VW Bora with the driver, McKenna, "beeping his horn profusely".
She pulled the car in at Main Street, and as Gda Robinson spoke to McKenna, his sister Amy walked over, shouting foul language.
Thomas McKenna recorded the incident with his iPhone as his sister resisted arrest and he pulled Gda Tyrell's arm as she tried to help her colleague.
When arrested, he put his hands in his pockets, became "very violent," and was pepper- sprayed.
Gda Robinson said that when she asked McKenna about beeping, he said: "What horn are you on about?"
She alleged that Ms O'Donnell said "I had no f**king right to arrest her daughter" and tried to pull her daughter away.
McKenna said he had been beeping to get his sister's attention and was not a kilometre away from her as gardai said.
Judge Jones said the situation had been "totally avoidable" and the actions of the gardai were "proper and necessary".