Repeatedly, prosecutors tried to get the 33-year-old right-wing extremist to describe his devotion to the online game in the years leading up to his July 22nd 2011 attacks, but Breivik mostly would not talk.
"'World of Warcraft' has nothing to do with July 22nd," he insisted.
"The prosecution is just trying to ridicule me," he added, getting so exasperated by prosecutor Svein Holden's questions that he even turned off his microphone at one point.
Breivik previously said he took a year off in 2006 to dedicate himself completely to playing the multi-player game set in a fantasy medieval world and generally considered non-violent, and that he had spent up to 17 hours a day at it.
On Wednesday, the Oslo district court heard evidence that Breivik had continued to play intensively until February 2011, only months before the July 22nd attacks he has admitted carrying out.
That day, he first bombed a government building in Oslo, killing eight people, before going on a shooting rampage on the nearby Utøya island where the ruling Labour Party's youth wing was hosting a summer camp, killing another 69, most of them teens.
Holden told reporters after the trial day ended that his questions had not been aimed at blaming the game for the attacks but had been meant to shed light on incoherencies in Breivik's explanations and to help determine the tricky question of his sanity.
Breivik has said that as of 2007 he had been working "full-time" writing his manifesto — a 1,500-page ideological tract detailing his hatred for multiculturalism and Islam.
But in 2008, he also wrote that he was playing "World of Warcraft" non-stop.
Faced with this apparent contradiction, Breivik defended himself, insisting he had juggled between writing his manifesto and playing the game.
"You are a prosecutor full-time, and yet I'm sure you have hobbies when you go home at night," he said to Holden.