If someone asks you to leave him/her alone, do so. Do not continue to page or speak to someone who has asked you to leave him/her alone. Do not send continual @mails to that person. This is especially true if they are accusatory, sexual or abusive in nature. Harassment of someone is a serious offense and can lead to site banning. Do not put yourself in this position.
If you are being harassed by someone, file a complaint with the +complain function. Keep in mind that we will need some sort of proof of the accusation, such as logs including dates/times of the offense(s). Without the supporting documentation, it becomes a "he said, she said" situation and it is impossible for us to prove wrong-doing. These complaints will be looked into promptly, although the results will be more definitive if you have the necessary supporting documentation.
Do not make such accusations lightly. If it is found that you are making these complaints against another person erroneously, utilizing the rules to harass a person in turn, you will fall under the same Harassment rules.