I've never had a boyfriend but...?

Several people at my school call me a "slut" and a "skank." I don't know why since I've never even had a boyfriend. I asked one of my friends why people would call me this, and she said "Well is cause you're gorgeous, popular and I'm pretty sure a lot of guys like you. Those girls are just jealous and it makes them feel better." Even if what she said is true it's hard to convince people that your not a sl*t or whatever, and I don't want people just going around thinking this about me. I don't know why these girls would think that or say that. I don't have a boyfriend, no guys have ever asked me out and I never did anything to hurt these girls, I don't even know them. I hear from my friends that some guys they know really like me and those guys act kinda shy around me (even though they're normally out-going) but does that really justify calling me these harsh names?