What common prostitution story did Theroux hear numerous times during his travels and how did the story told in Laos differ?

Theroux had been regaled several times with stories of men paying prostitutes only to discover that the woman was actually a man in drag. The tales generally ended with the john fleeing in shock, even though the men seemed strangely willing to share their embarrassment with Theroux. By contrast, the man who told this story in Laos admitted to later kissing the prostitute at the bar and insisted he would look the man up if he ever went back to the bar.