A woman"old enough to know better" has been fined for flashing her bare bottom and spanking herself in front of a crowd at the Gold Coast Indy.

Lucinda Dorothy Dimond, 37, of Main Beach, pleaded guilty in court yesterday to public nuisance over her balcony performance on October 26, the Gold Coast Bulletin reported.

Police prosecutor Acting Sergeant Mike Campbell said Dimond should have known better.

Sgt Campbell told the court Dimond pulled up her short denim skirt and exposed her bottom before "spanking it."

It appeared she was not wearing any underwear.

"She performed this exhibition three times where she would re-enter her apartment and return to the balcony to expose her bare buttocks and spank herself," said Sgt Campbell.

"With the amount of public education regarding this nature of offending, it is very disappointing to see a relatively mature lady behaving in this manner, not once but three times effectively."

Dimond's barrister Chris Rosser said she had been pressured from the crowds.

"As a custom at Indy, crowds gather at high rises. She could hear all the chanting and yelling out. If you are a woman on a balcony you get accosted," he said.

"She said she was wearing underwear, she says she was definitely wearing underwear."

Magistrate George Wilkie told Dimond: "I'd have thought you are a bit past this behaviour at your age," before fining her $400.