A man who was previously jailed for killing his father started shouting obscenities at gardai after they tried to arrest his own son.
Gary Waters (45) was directed to leave the area by officers, but he continued to hurl abuse.
Judge David McHugh convicted and fined Waters €100.
The judge said he understood how a father might try to protect his son, but added that Waters could not break the law.
The defendant, of Valeview Gardens, Finglas, admitted threatening and abusive behaviour and failing to follow directions of gardai when he appeared before Blanchardstown District Court.
The incident happened near his home shortly after 11pm last October 1.
Gda Brian Masterson told the court he was helping his colleagues to deal with a juvenile when Waters came out of his home and tried to interfere in the matter.
Gda Masterson said Waters started shouting obscenities at gardai, and he was directed to leave the area but failed to do so.
His behaviour also caused other people to come out of houses and shout at the officers.
The court heard that Waters had eight previous convictions, and had received a seven-year sentence for manslaughter in 2004.
In that case, Waters stabbed his father 19 times in the neck and head after he heard him talking about sex abuse allegations.
Defence lawyer Jennifer Jackson said that Waters "got involved in something that he shouldn't have".
The court heard that Waters was "a father who was trying to protect his son".
Ms Jackson also said that her client wished to apologise to the gardai involved for his behaviour.