We all know how nerve wrecking it can be to tell someone that we have a crush on them, or that we like them as more then a friend. I for one could never find the courage to tell a guy that I like him, because I'm so afraid of getting hurt, and because of general shyness. It's a huge risk to tell someone how you feel, because you're really putting your feelings on the line, and if it turns out they don't feel the same way, you'll feel absolutely crushed. So when it's reversed on you, and someone is telling you that they like you, the last thing you want to do is hurt their feelings, even if you don't like them in that way. And if that person is a friend, it can be even harder, because you don't want to lose the friendship. In any case, you just might not want to feel as if you're being mean to them, as you know that it must have taken them a lot to tell you that. It may seem like it's easiest to stretch the truth and say "I like you, but I'm not ready for a relationship right now", rather then just saying "I'm sorry, I don't like you like that". This way you don't have to date them, but you don't hurt their feelings. But believe me, it's much better just to be straight up and tell them the truth.
You may be flattered that someone likes you, along with not wanting to hurt them, but if you don't like them back, and you really can't see yourself being in a relationship (or being happy in a relationship) with them it's best to just tell them the truth. Sure it's nice to have someone like you, but if they think that they may have a chance and they start getting flirty, things can get really uncomfortable really quick. Thinking you feel the same way, they might be flirty with you, waiting for that day you are ready for a relationship to come. They won't know that it's making you uncomfortable if you keep flirting back, or unless you tell them that you don't like them like that. If they think you like them, they'll think that you like it, and they'll keep persisting with it, having no idea of how creeped out or uncomfortable you may be. No matter how flattered you are, if you don't like them back, and they keep flirting, flattery can turn to resentment towards them, and wanting nothing more then to avoid them. This certainly would not help out the friendship you had with them before. I learned that the hard way.
I am not perfect, and I have gotten myself into this mess before. During my sophomore year of high school I became good friends with this one guy from my school (although it's not his real name, let's just call him George). I had talked to him a few times when I was in 8th grade, but never really all that much until I got into 10th grade. George had always seemed to be really nice, and he was super friendly. It was nice to have a guy friend to talk to, especially with him being a really good listener. It was also nice to be able to talk to a guy that I knew in real life that wasn't a jerk like most of the guys at my school. It was all good, until... I found out that he liked me as more then a friend, but I didn't like him in that way. Nor was I really ready for a relationship, as it was pretty soon after my break-up from my 2-year online "relationship" with Charlie. However, I for sure did not handle it the right way at all. A combination of feeling a bit flattered that a boy liked me, not wanting to hurt his feelings, and not wanting to lose a friend took over me, and I told him I liked him too, but I wasn't ready to date anyone because of what happened with Charlie. So he told me he'd be there when I was ready, and from there... the conversations got uncomfortable and uneasy for me.
The fact that I didn't tell him straight up that I didn't like him in that way, and only liked him as a friend made him feel as if he had a chance, even though he didn't really have much of one. He started to get a little more flirty, and I went along with it most of the time because I didn't want to hurt his feelings. I tried to avoid the flirty conversations as much as possible by talking about school, teachers, or anything else, but it would always come back up. It got to the point where every time he would text me I would sigh, and sometimes not answer it and find an excuse later. And although all of our flirting was over the phone and through text, never at school or anywhere face to face, it got to the point where just being around him made me uncomfortable. He was a senior that year, and I couldn't wait for him to graduate so I wouldn't have to see him anymore, and that's when we began to lose contact. He wasn't a bad guy at all, but his flirting really bothered me and drove me away from him. Had I just told him that I only liked as a friend from the beginning, if he was as nice as he seemed to be, he may have laid off and accepted it, and maybe we would still be good friends. I really regret the fact that I didn't just tell him, as I could have saved myself the discomfort and regret, and him the time and effort.
So as hard as it may be, it's always better to tell the truth. It'll save both of you a lot of time, and emotions in the long run. It will hurt their feelings, but there's no avoiding that. It would hurt them even more if they found out that you never actually felt the same way. You don't have to be mean and nasty about it, just tell them that they are a great friend, and you do care about them and want to be their friend, but you don't want a relationship with them. Keep in mind that if they're a friend they may have the same worry about ruining the friendship. If they truly do value your friendship they should understand it, but they may need some space for a while. It may even be best to keep a little distance for a while so that they can get over you. It may sting a little, and it may even sting a bit to see them get over you and find someone else, but it's for the best. Both of you would be much happier with that, rather then trying to make something you don't want work.
The other person may not always be able to accept that you just want to be friends, and can't settle for friendship. If this is the case, it's best for both of you that you end the friendship. Trying to keep a friendship with someone that only wants more will only hurt both of you. They may also keep trying to get you to like them, and won't stop flirting, even if you tell them to stop. You may even find that arguments come easily, and fights are constant. It's hard to keep a friendship when fights are coming almost daily. If you can't agree to be friends, and only friends, it may not even be worth it trying to save the friendship.
If you tell the other person to leave you alone and they won't, or if they start threatening you, you need to tell someone. If they won't stop texting or calling, don't answer them. Block them on any social networking sites you're on so they can't message you. If they keep persisting, tell someone you trust so that they can help you. If they physically follow you around, roam around your home, threaten to harm you in any way, this is a serious matter that needs to be reported to law enforcement immediately. Don't wait until it's to late. Hopefully, and more then likely, it will never come to that, and the other person will lay off, even if they are hurt or mad they'll get over it. But there are some really bad, and creepy people out there. Never get into a relationship because of a threat. If they are willing to hurt you for any reason, they aren't the kind of person you want to have anything to do with.
Yes, telling someone you don't feel the same way about them is hard. You know it'll hurt them and break their heart, and that it could mean losing a friend, but it'll be best for both of you. It might even save your friendship before you get driven away by unwanted flirting, and it'll save their heart in the long run. You don't wanna get into a relationship that you hope from the beginning won't last. You can't keep it going forever, and you don't wanna wait until they break up with you, or do the exact opposite... :S Yeah.. perhaps telling the truth form the beginning would be better.