Norwegian Tommy Hol Ellingsen, 28, and his Swedish girlfriend Leona Johansson, 21, showed up in court dressed as small children, but with pictures of genitalia sewn onto her clothes, Norwegian daily VG reported on its internet site.
Then, during a court recess, Hol Ellingsen dropped his pants and flashed the surrounding press.
"I seem to have dropped my pants," he was quoted by the paper as saying.
The couple were in court on Tuesday to contest the 10 000-kroner fines they were each issued after having sex for nearly 10 minutes on stage during a concert by The Cumshots at the Quart music festival in the southern city of Kristiansand last July.
The stunt was later discovered to be a pre-arranged public relations gimmick to raise money for the couple's environmental group, called Fuck for Forest, which raises money for organisations working to protect the rain forest.
Among other things, the couple have launched a pornographic website where visitors to the site can pay $15 a month to view videos of them making love.
The couple's lawyer reportedly argued that their behaviour was permissible under Norwegian laws on freedom of expression.
The two have claimed in police interrogations that the whole Cumshots band and Quart festival management had been aware of their plans to fornicate on stage.
Three of the five Cumshot band members also appeared in court on Tuesday to challenge their fines, while the two remaining band members who had accepted their penalty showed up as witnesses.
Quart festival representatives have meanwhile rejected a 50 000-kroner fine for the incident, and are expected to argue that they were unaware of the planned sex stunt when they appear in court next week.
Having sex in public is illegal in Norway and carries a maximum sentence of a year in prison.