One of the Australians was also coaxed onstage and spanked by two girls waving sponge paddles while the audience cheered.

"The majority of our customers will be a part of some show during their event," said Jermaine Holliehead, founder of Thailand Bucks and Hens. "Fifty percent of the time, (they) will also wear fancy dress throughout the evening. Usually a French maid or some sort of drag queen costume."

After watching nude lesbians cavort on stage, while a naked girl showered nearby behind glass, the tour went to another Nana bar.

"It's crazy fun," one of the group said.

Capping their evening, the Aussies arrived at a popular upmarket Sukhumvit Road nightclub, and were escorted to an exclusive table.

Holliehead says his tours, established more than a year ago, have served more than a thousand customers, 75% of them male.

Their favorite theme is "one crazy party night, with their best friends, before they get married," he said.

Holliehead didn't provide information about prices, saying each event differs, but all tours include transportation, a guide and lots of alcohol.

The company runs tours elsewhere in Thailand, including female-only Hens nights, usually on Koh Samui or Phuket Island.

Critics not impressed

Not everyone is happy about these tours.

"Sex tours to the nightlife in Bangkok, or anywhere, are harmful to both the tourist and the women," according to Annie Dieselberg, the American CEO of NightLight International, a Christian-based organization active in Bangkok, Los Angeles, Atlanta and elsewhere.

The organization is working to end commercial sexual exploitation.

"Sex tours normalize the exploitation of women, and grooms men to believe they have the right to be entertained at the expense of the women," Dieselberg said after hearing about the Bangkok Hangover Tour and Thailand Bucks and Hens.

"I have spoken to several thousand women in prostitution, from over 12 nations in the last 14 years, and 99% of them hated this work and were only doing it because they saw no other way of meeting the family economic needs and pressures.

"As time passes, the women deteriorate and lose sight of their true identity and dreams for life.

"Many become [suicidal razor] cutters, and many become addicted to alcohol and drugs to cope with the shame and self-hatred," Dieselberg said.