Is it OK to avoid or ignore a person I don't get along with?
Since the commandment of love of neighbor is absolutely universal, it is harder to interpret than a mere negative commandment. A negative commandment such a "Thou shalt not commit adultery" is a commandment obvious in its application. "Love your neighbor as yourself" may not be as clear. This is the Christian sense of your question.
If the reason you don't get along with the person is because he or she seeks to lead you into sin, then certainly you should avoid the person, at least in the context in which there is a temptation. If the person has wronged you, and you are hurt or angry, then you need to be more careful about avoiding or ignoring. Our Lord says, "Love your enemies, pray for those who persecute you." So we know that in any case we should seek to do good to those whom we find offensive, or who have hurt us. This may mean avoiding contact for a time, but it also may mean seeking out an opportunity to speak frankly and calmly with the one who has offended us to seek reconciliation.
Sometimes a relationship is unhealthy psychologically—for example, what therapists would call a "codependent" relationship. In such a relationship, there may be a place for some separation in order to overcome the exaggerated attachment. But if you simply "don't like" a person who has done you no wrong, then you need to look at what in yourself refuses to accept the different character of another human being and try to become more flexible in your evaluation and treatment of others.
In the end, it still is pretty simple: treat others they way you would like to be treated. Ask Our Lord to help you love others the way he would have you love them.