A bus driver called his partner's estranged husband "a pussy" and assaulted him by punching him in the face.
Martin Anthony Cormican (52) had denied the allegations, claiming John Tyrell called him a "bully boy from Baldoyle" and he simply defended himself.
A court heard Cormican is Mr Tyrell's estranged wife's new partner, while Mr Tyrell's new partner was previously in a relationship with the defendant.
Judge Dermot Dempsey ordered Cormican, who has no previous convictions, to enter into a peace bond for two years.
Cormican, of St Cronan's Avenue in Swords, was found guilty before Swords District Court of assaulting Mr Tyrell.
An allegation Mr Tyrell assaulted Cormican was dismissed by the judge.
Mr Tyrell said he was speaking to his wife at St Cronan's Avenue on April 10 when Cormican called him a "pussy" and told him to "f**k off".
He said he told him to back off but Cormican kept coming and swung a punch at him.
He alleged Cormican swung a second punch at him, but missed, and he picked him up and threw him to the ground.
In his evidence, Cormican claimed Mr Tyrell threw a punch at him. He said he got Mr Tyrell in a headlock but he was thrown to the ground.
Finding Cormican guilty of assault, Judge Dempsey said he believed Cormican was the instigator of the incident.