Estibaliz Carranza, a 34-year-old Mexican-Spanish woman dubbed the "Ice Lady" by Austrian media, told a court that both men had "demeaned" her; her ex-husband by yelling at her and making fun of her poor German, her lover by being unfaithful.
In both cases, she said she had shot her victim with a .22 calibre Beretta pistol, chopped up the body with a chain saw, put it in a freezer at the parlour, and eventually buried it downstairs in the cellar, the Austria Press Agency reported.
Prosecutor Petra Freh described the defendant, who appeared before a packed court wearing a grey dress and flanked by prison guards and her celebrity defence lawyer Rudolf Mayer, as "ice-cold" and a "ticking time bomb".
"It's clear that the defendant has two faces," Freh said, warning that Carranza could kill again.
Carranza told the court the nature of her husband, Holger Holz, had completely changed after their wedding, and that matters had got worse when they were evicted from their apartment and moved into the ice cream shop, and Holz joined the Hare Krishna movement.
"He slept until 10 o'clock and came at 11 o'clock. We had no ice cream. He did nothing. He didn't want to get a grip," she said.
Even after she started a relationship with ice cream machine salesman Manfred Hinterberger and divorced Holz, he refused to move out, she told the court on Monday.
One Sunday, after an argument about the issue, she said she had shot Holz twice in the back of the head and once in the temple as he sat at his computer.
Mayer, who unsuccessfully defended Austria's most notorious living criminal Josef Fritzl in 2009, said the psychiatrist's report on Carranza showed that her danger to society could be reduced "to zero" with proper treatment.
He warned the jury not to be influenced by negative portrayals in the Austrian media, which have had a field day with the story of the Hispanic immigrant and her many lovers.
"The defence is determined ... that the jury do not accept the picture that been has given of her as ice-cold, unfeeling, unscrupulous, capable of anything, but rather that they recognise what is behind this facade," he told journalists.
Fritzl was sentenced to life imprisonment for incarcerating his daughter in the basement of his family home for 24 years, during which he physically assaulted and raped her, fathering seven children.
Hinterberger left Carranza shortly after her divorce but turned up on the doorstep of the salon with a suitcase a year and a half later after being thrown out by his girlfriend.
She said she had taken him back, but then found sex messages on his phone and his profile on a dating site.
On the way home from an evening out with friends, where he had flirted with another woman, she had wanted to talk about it but he had simply shouted at her and then gone to bed, she said.
"He turned to the wall and began snoring. He just turned around and that was the end of the matter for him. I was so furious," Carranza said.
She then described how she had reached under the mattress for the same pistol she had used to kill her ex-husband, loaded it, and shot him in his sleep.
Again, she chopped up his body, deep-froze the parts and eventually buried them under the icecream parlour, where they were found by chance during maintenance work last year.
Carranza was extradited from Italy, two months pregnant by another man, to face charges in Austria.
The trial is due to run until Friday.
