Hm, someone who made my life a living hell, or was really awful to me.
When I was in seventh grade, there was a girl who showed up at my school. We became fast friends, and I thought we were best friends. However, she was busily trying to infiltrate the so-called popular crowd, unbeknownst to me. Anyway, once she got in with them, she dropped me like a hot potato. It was a real shock to my system. You know how when you move to a new city you might rent for awhile until you figure out where the cool part of town is? Yeah, well I was her rental. From what I could tell, she remained a bitch for the remainder of her time in our town.