Well the legal definition of harassment requires systemic or persistence to qualify outside of separate circumstances. If If someone were to heckle or catcall you outside of a bar or in a movie theater once that isn't harassment. Following you down the street persistently and heckling or cat calling after you told them get lost or organizing a different person to heckle you every day would qualify as harassment.

A coworker, boss, or anyone in a privileged position like a doctor or police officer sexually harassing you once is unacceptable legally.