The defence in the 'Mr Moonlight' trial was prejudiced by "side issues" and remarks about "who was going to be smelling somebody else's knickers", the Court of Appeal has been told.
Lawyers for killer Patrick Quirke claim the trial judge gave too much leeway to the prosecution and let evidence be admitted even though it was unproven or of little or no probative value.
They also complained the defence team was put on the back foot by the repeated late disclosure of evidence.
These were among 52 grounds of appeal as they sought to overturn Quirke's conviction for the murder of love rival Bobby Ryan in 2011.
His counsel, Bernard Condon SC, said the approach adopted by trial judge Ms Justice Eileen Creedon and the prosecution had led to "enormous dollops of prejudice" being heaped upon his client.
He argued irrelevant and prejudicial material went before the jury. This included evidence from his former lover Mary Lowry, in which she alleged Quirke stole knickers from her clothes line.
According to Mr Condon, Ms Lowry was an "extraordinarily compromised witness" who gave inconsistent and unreliable evidence.
Married farmer Quirke (51), of Breanshamore, Co Tipperary, was jailed for life last year.
The prosecution alleged he carried out the murder so he could rekindle an affair with Ms Lowry, who was in a relationship with Mr Ryan at the time.
Mr Ryan disappeared on June 3, 2011, after spending the night at Ms Lowry's home at Fawnagown, Co Tipperary. His body lay undiscovered in a run-off tank for two years.
Mr Condon said Ms Lowry was an important witness and accounted for 115 pages in the book of evidence.
He said he identified portions of 40 of these pages which he believed should not have been put before the jury.
Some of the passages were irrelevant, some lacked an evidential basis and some were more prejudicial than probative, Ms Condon claimed.
While the trial judge ruled out some of the matters identified, she left in others, despite objections.
Mr Condon said part of his reason for seeking to limit the material put to the jury was so the case would not "degenerate into a family law dispute".
He said adult relationships could break down and were often accompanied by bitterness. In these circumstances care needed to be exercised so that a line wasn't crossed where the breakdown became the focus of the jury, he said.
He said the prosecution could have limited the chance of prejudice occurring.
Mr Condon said evidence from Ms Lowry that Quirke was acting strange at his son's confirmation was also prejudicial, while evidence of financial arrangements between Quirke and Ms Lowry were allowed go before the jury even though they were not proven.
He also claimed references to Quirke being depressed were "very stigmatising".
Mr Condon also said gardaí made prejudicial comments that should not have been heard by the jury.
This included a comment by a garda that Quirke had "cash on demand and sex on demand" from Ms Lowry.
The appeal, before Mr Justice George Birmingham, Mr Justice Patrick McCarthy and Ms Justice Isobel Kennedy could last for four days.