Report it to your employer. Generally, if an employer has a policy against harassment and a procedure for reporting it that is published to the employee, the employer will not be responsible for sexual harassment unless and until the employee reports it. If you feel you are being subjected to unlawful harassment, look in your company handbook or the break room bulletin board for a notice procedure. If you do not see one, ask a supervisor or someone in human resources for how to report it. If all else fails, report it to your supervisor or, if he/she is the problem, their supervisor. Also, report the harassment in writing, keep a copy, and make a written note of when and to whom you report the harassment.
There are types of unlawful harassment for which the employer will be responsible without a report being made. These include the situation where your job is brought into the harassment. For example, if a supervisor requires you to go out on a date (or more) to get a promotion or keep your job, this is a type of harassment for which the employer will be responsible for regardless of notice. However, in most every case, it is still a good idea to report the harassment to your employer to give it the chance to fix the problem.