Why am i getting called a skanky ***** for dating a guy one grade lower than me?

So last night, I was out with some friends at the skating rink. I was having a blast and everything was all good until some random chick came up o me and ask, " Are you dating so and so?" I answered back yes...and then her and her little group (2 people) laughed as if it were discusting to even be dating him...? Huh? I didnt get it at all...so I went away from them. This girl did the same thing to my best friend when she found out that my friend was dating a guy she had a crush on. She went around the whole rink telling girls that my friend was a whore for dating him...shed look, and point...and even stalk my friend and her boyfriend. So... another hour had passed..and I figured out that she had spread rumors almost all over the rink about me and him dating to where even a girl in 4th or 5th grade started calling me a skanky *****??? Why am I getting called a skanky ***** for dating a guy younger than me? It doesnt make any sense...and I didnt even know the little girl.. and the reason she only called me that is because the girl that had spreaded the rumors had obviously told her that i was dating him....what have i done wrong? .....