Liam Lloyd Warriner, 22, a barman from Sydney, pleaded guilty in the Brisbane Magistrates Court to being a public nuisance on Oct. 24.
Warriner was arrested after he dropped his shorts and underwear and pointed his butt at the queen as her motorcade traveled along Kingsford Smith Drive. He had the Australian flag clamped between his buttocks at the time.
The barman always maintained he had never exposed his genitals.
"I reveal the [Australian] flag stuck between my (butt) cheeks and then I slap my (butt) while I was yelling at [the queen's husband] Prince Phillip," he said. "The queen's car was actually moving quite fast. I couldn't exactly keep up with it."
Police Sgt. Troy Newman said Warriner had shown a selfish attitude to score a political point during a formal and respectful occasion. He also said the accused had shown disrespect to the flag.
Outside court after being fined, Warriner said he didn't regret what he'd done, adding, "I'm a proud anti-monarchist."