Say no. Do not flirt. Do not laugh it off. Do not send emojis to your harasser. Do not engage your harasser in long exchanges of text messages. Do not send your harasser pictures of yourself. Sexual harassment law requires that the sexual harassment be "unwelcome." It is important that your harasser knows that his conduct is unwelcome. Tell him that his conduct offends you. If you are uncomfortable saying that, then tell him to stop. Redirect sexual or overly personal communications from your harasser to work-related matters. Say no to invitations for dates or other personal interaction outside of work. Direct communication, preferably in writing, is best.
Report sexual harassment to your employer. This is critical because your employer will not be legally responsible for sexual harassment by a co-worker, client or customer unless it knows or has reason to know about the harassment. Tell your supervisor. If your supervisor is the sexual harasser, tell your human resources department or some other person at your company who has the power to stop the harassment. Tell them in writing and keep a copy of what you submit. If your written complaint is just a summary, then say that and offer to provide the full details later. You want to create a written record of when you complained and what your employer did in response to it. You employer may very well have a sexual harassment policy that tells you what to do if you have experienced sexual harassment. You should follow this policy and even cite it in your written complaint. If you do not communicate your concerns about the sexual harassment, your employer will later argue that it would have stopped the sexual harassment if it had known about it. Therefore, reporting the sexual harassment is very important to show that your employer knew what was happening.
Write it down. As soon as you experience the sexual harassment, write down exactly what happened. Be specific: write down dates, places, times, and possible witnesses to what happened. Keep screenshots of any sexually harassing text messages. If they are on your work phone, send them to your personal email address. If your sexual harasser is also harassing your co-workers, ask them to write down what they saw or heard. Be as accurate and objective as you can. Keep your notes and evidence at home or in some other safe place where you will have access to it in case something suddenly happens at work.
Keep your work records, including your performance reviews and positive comments about your work. If you do not have copies of these documents, in Pennsylvania, you have a right to inspect your personnel file. You should either make copies of relevant documents or take detailed notes of what is in the file, if you are not allowed to copy the contents.
Talk to others. If you can do so safely, talk to other people at work about the harassment. You may find witnesses, allies, or others that have been harassed by the same person or who would be willing to help support you. Tell supportive friends, family members, and colleagues about the abuse. Telling others about the harassment not only can give you much needed support, but it can also be important evidence later.