Ignore the individual who you extremely unsympathetic. Don't see him, don't answer his calls and messages. Pretend to be that person for you there. Sooner or later the individual has to understand that it does not wish to communicate, and to stop bothering you. If not, then you got a particularly stubborn person or a person who does not understand such subtle hints. In such situations you can try another way.
Sharply limit your communication with unpleasant individual. When you see him pretend you're in a hurry. Constantly refer to urgent matters. Answer in monosyllables, Yes or no, do not ask themselves any questions. Gradually, your dialogue will become a monologue, and people just will not be able to support it. Conversation runs out, and maybe the individual will realize that he is not interested in you. Do not maintain eye contact with the person. Look away at his feet. Talk with him on the phone. In every way show his contempt and employment. Of course, such treatment may hurt the individual, but he will be behind you once and for all.
If you nag the individual feels towards you strong sympathy, to get rid of it is not so simple. When you know what you are attracted to, you can change a specific trait of their character or appearance, and to adjust the behavior. Seeing you radically change your annoying fan can ice you, leave you alone and find a new object for his obsessive courtship. Be very careful with such people. Any manifestation of simple good human relations they are willing to accept for the promotion of their actions, and then they become more forceful. So it is important to be stressed cold and indifferent person.
Sometimes you got people that you can't just dismiss. For example, you are forced to communicate with him on duty, or you are bound by family ties. In this case, ignoring will look pretty strange, but rudeness is generally not worth going. You have two options: either to suffer in silence and try to distract myself with more pleasant thoughts, when you have to communicate with this individual or speak to him. Call the person on candid conversation and calmly explain that his behavior is unacceptable. Maybe you will be able to influence the individual and to establish a relationship with him. It all depends on how much you will be diplomatic.