Multnomah County Circuit Court Judge David Rees ruled Wednesday that Brennan's act was one of protest and therefore, protected speech.
Multnomah County Deputy District Attorney Joel Petersen argued that Brennan's strip-down was an act of indecent exposure.
"I was aware of the irony of removing my clothes to protect my privacy," Brennan said from the witness stand on Wednesday.
On April 17, Brennan arrived at the airport intending to take a business trip to San Jose, Calif. He works with groups in Silicon Valley and flies out of Portland International Airport about once a month.
When he reached the gate, he declined to go through the airport's body scanners, instead choosing the alternative metal detector and body pat-down. After the pat-down, Transportation Security Administration officer Steven Van Gordon detected nitrates on the gloves he used to check Brennan.
"For me, time slowed down," Brennan said. "I thought about nitrates and I thought about the Oklahoma City bombing."
Brennan said before his trial that after months of angst every time he went through security, the nitrate detection was the final straw for him, a wordless accusation that he was a terrorist.
So he took off all his clothes.
A TSA agent stacked plastic crates high onto several carts and positioned them around Brennan. Port of Portland police arrested Brennan and took him to the Multnomah County Jail.
Brennan, 50, demanded a jury trial in early May, but was turned down.
Brennan insists he didn't come to the airport intending to protest. He had called the Port of Portland -- which operates the airport -- a year earlier to ask whether Oregon's rules involving nudity applied at the airport. Brennan said he was told that they did. Brennan said in court that he asked because he had considered nudity as an act of protest, but hadn't found cause to strip down.
The law says that naked people are only breaking the law if they're having sex in public or got undressed "with the intent of arousing the sexual desire" of another person.
But if Brennan truly was acting in protest, Petersen asked, then couldn't anyone be arrested while naked make the same claim?
"Any person naked for any purpose will be able to say it was protected speech," Petersen said.
Portland would be an interesting test case for such a question. After all, this is the city with the World Naked Bike Ride, before which police simply send out a light admonition to "all riders at least wear a helmet and shoes."
As Brennan left the stand Wednesday, he said that his protest was also intended to give the TSA an idea of the effect its policies had on travelers, especially the body-scanners that produce images of passengers without clothes on.
"I wanted to show them it's a two-way street," he said. "I don't like a naked picture of me being available."