I would ask them questions completely unrelated to their field of work. As well as very personal questions that would make them extremely uncomfortable. The awkward silence created by their unwillingness to answer would be met only with a wide-eyed, curious stare. I'd continue to stare until they answered, or left.
Questions such as: How often do you have BMs? Do you have any kids, and if so, are they hot? Are you capable of satisfying your husband/wife? If not, may I have a go at it (wife, not husband)? Have you ever worn women's underwear (male-only question)? N00dz?
Things like that. I could go on...