hankey-pankey

 Professional cant; the chatter of conjurers to divert attention from their tricks; hence, jugglery.  [1913 Webster]

 Illegal or unethical behavior, usually surreptitious; as, the boss got suspicious when profits seemed lower than expected, and hired an investigator to see if any hankey-pankey was going on.  [PJC]

 Extramarital sexual relations, especially adultery.  [PJC]