Remain calm during the conversation. Loosing your cool can make the conflict escalate, reports communication coach Preston Ni on Psychology Today. Ni suggests counting to 10 before initiating a conversation. Doing so will help you to relax and mentally prepare for what you are about to say.

Consider the other person's feelings and perspective, writes Ni in his 2013 article "Ten keys to Handling Unreasonable and Difficult People." Thinking about how she will feel when you tell her to back off will help you to stick to your determination to be polite. For example, you know that your date has a crush on you, but you don't feel the same way and want her to stop calling. Put yourself in her position and craft a conversation starter that is sensitive to her emotions.

Clarify consequences for repeat behavior, suggests Ni on the "Psychology Today" website. Being polite doesn't mean that you need to sound mousy or give in to the other person's wants.

Listen to what the other person is saying. Even though you're the one who is bringing up this issue, being an active listener can help you guide the conversation and politely make your point in the context of the other person's thoughts and feelings, according to the article "Effective Communication" on the University of Maryland's University Health Center website.

Be honest, but not brutal. Tell the other person you want him to leave you alone. Licensed psychologist Clifford N. Lazarus writes in his article, "Simple Keys to Effective Communication," being honest and to the point is necessary to completely communicate your needs. This won't leave wiggle room for him to try to talk to you or contact you again. For example, if your ex keeps messaging you on social media, tell him that you've moved on and think he should do the same too.