It has happened to me 2X so far. The first time was when I was a Senior in HS.
1) The japanese chick (2 grades below, average looking) liked me, but I wasn't into her. I hung out with her for a total of 2 hours and it was in a group. She got real clingy next time I saw her and the time after that she came with a group of my friends to hang out when it was time to leave she wouldn't and I had to remove her from my house. I didn't lead her on either I said "I don't like you, go away" and she still hung around for a few months until I got rod of her.
2) I was a senior in college and this asian chick (she was kinda cute too, but I just wasn't into her there was something odd about her) in my International Business class would hover around me and kind of stare sometimes. I just ignored her and dropped the class.
I kind of believe in Karma now because I haven't had a decent date since I was a freshman in HS.
hopefully all that is going to change when I do the MBA program this fall.