How can i ditch an annoying friend?

[Stephanie]

So, I hung out with this person once, and after that they started talking about how we were best friends, should get tattoos proclaiming it, and hang out all the time. Needless to say, this person in super clingy, talks all the time, asks the most stupid questions and doesn't seem to understand anything other than pop culture. I tried simply ignoring, but the person called me over 100 times in one day, messaged my facebook, called other friends asking about me, and even showed up at my house! It's hard for me to be mean to someone unless they are actually mean to me, and I feel bad for the person because I am the only person who gives this person any kindness. The person begged me to hang out with them again, which I did, and is now psyched for us to be bffs and hang out all the time! help, please? ps. when I say I have other plans the person seems to think its acceptable to invite his or herself along...
To my understanding, the person has little experience managing friendships and has said that he does look up to me, and that he is so much happier since we have become "friends."