Some people just can't take a hint. Maybe a recent ex is calling you everyday to find out what's up. Maybe a man from your past instant messages you every time you get online. Maybe you went on one date with a guy, didn't connect, and then made the mistake of saying "we should do this again" -- and now you get a text from him every day. No matter which guy in your life is giving you the problem, here a few steps to make it clear that you don't want to communicate.
First, be sure that you aren't encouraging contact through your behavior, even if you are doing so simply because you "don't want to be mean." If you stop replying to phone calls, texts and messages, you may solve your problem fairly quickly. Use this tactic in particular if the guy is someone who you met only very briefly (one date or on a night out). Of course, if the guy is someone you used to spend a lot of time with or know well, simply ignoring him without telling him why might be hurtful.
If it is a situation that requires communication, be straightforward and clear. Women often like to "soften the blow," sometimes to the extent that the guy doesn't really know what's being asked of him. Make sure that you're making yourself understood: If this is an a recent ex, tell him you need your space to heal. If necessary, be specific about what behavior has to stop -- contact includes virtual behavior, such as emails and text messages. If this is a man from your past or a guy you don't know very well who can't seem to take a hint, tell him that you don't want to be in contact. You can say something like, "I don't want to be hurtful, but this isn't working for me and makes me feel uncomfortable. I would like you to stop contacting me." Don't offer explanations that leave hope for future contact ("I really like you, but..." or "I'm not ready to date" or "I don't know you that well") unless you want future contact.
Take more authoritative steps if the behavior continues. Block his phone number, block him on instant messaging and remove him from your online social network. If you run into him in public often, change your routine. If his behavior disturbs you or frightens you, then this could be stalking or harassment. You can tell him that you will contact the authorities if his behavior doesn't stop, but only tell him once -- continuing to contact him will encourage his behavior. Keep evidence of his contact with you, and call the police to register a complaint.