demi-monde       
noun [ C usually singular ] uk/ˌdem.iˈmɒnd/ us/ˈdem.iˌmɑːnd/
 (行为不被接受为正常或道德正确的人群)不入流社会
a group of people who live and behave in ways that are not traditionally accepted as normal or morally correct
  He descended into the demi-monde of alcohol and drugs. 他沉沦到酗酒吸毒的不入流社会中。 
 - More examples
 - He mixed with the bohemian demi-monde and ended up as the avant-garde publisher of Lady Chatterley's Lover.
 - Back in the 60s and 70s, she was a feature of London's demi-monde, an exotic name on the nightclub circuit, linked with a string of rock stars.
 - What lies beneath the cardboard veneer of Vegas glamour is a demi-monde of strippers, pornographers, drug dealers, waifs and runaways.
 - The director was a doyen of the shabby demi-monde of London's arts world in the Sixties and Seventies.