In the dating world, you'll sometimes encounter what we call "crazies". These are the guys that don't seem to get the hint that you're not interested and keep persisting long after the first rejection. So how do you brush off an unwanted admirer while still keeping your cool and sanity?
DO NOT respond The first rule of stalking is that you want to get a response out of your victim, even if it's a negative one. If you've told him clearly and in no uncertain terms that you're not interested and never will be, that should be sufficient. Don't reply to his texts, take his calls (hang up if he rings from a private number) or agree to meet him, even if he says he just wants to talk. You've already made your point, if he hasn't gotten the message by now, that's his problem, not yours.
Do call the police
The police are there to make sure that we live in a safe society. If you feel threatened and uncomfortable, if he hasn't stopped harassing you after a while and things escalate to the point where you don't even feel safe going down the road to the shops, then it's time to call in the experts. The cops deal with this type of situation all the time and can advice you on what to do. They might not be able to do much the first time you ring, but there will at least be a record of what's happened so they can take action next time.
Say what you mean Now girls, we all know that women often speak in riddles, often for fear of hurting the other person's feelings. A lot of us girls have been programmed to be nice from birth, but this is one situation where "nice" won't get you anywhere. Being honest isn't the same as being mean. After all, you are giving the guy obsessing over you the chance to get over you and start fresh, with someone that actually likes him. Be polite, but firm and tell him no thanks, you're simply not interested, not now and not ever.
The "I have a boyfriend" excuse
Some guys will only really see the light if they think you've found someone else. The danger with this is that if you are likely to see them again in the future, they'll find out you've lied at some point. But if this is a casual acquaintance or simply someone who works in the same building as you, then you can simply mention your "boyfriend Dan" at every opportunity. If that doesn't work, try rocking a fake engagement ring. It is a bit extreme, but if you needs must...