Seriously? At my highschool, a bunch of people LOVE Hello Kitty. I think it's stores like Hot Topic and other places in the mall that have made HK so popular. Also, you're in good company, because lots of famous celebs, like Katy Perry, Lady GaGa, Paris Hilton, and Kimora Lee Simmons also love Hello Kitty. So either the people making fun of you are dumb guys who are attempting to hit on you, or they don't know what they're talking about. Just ignore them!
Just tell them you don't care but people my age still love wearing her jewelry and saying their bad ass and stuff. I used to think it was lame but now it's catching on to me so just ignore them and show it off.
People who say that are usually trying to cover up what they like. They make fun of what other people like just to make them feel better about themselves, but on the inside, you should know that they are probably hiding something that they like, too. A very popular girl at my school used to make fun of me because I liked Hello Kitty too. I found out that she liked My Little Pony! I made her promise not to make fun of me again and make her friends stop teasing me or else her secret would be out. Yes, I was kind of blackmailing her >:) but it worked! She stopped making fun of me, and guess what? In our school, almost every girl has something with Hello Kitty on it. backpacks, shirts, pjs, notebooks, binders... You name it. Even stationary paper or whatever! HELLO KITTY ROCKS! Don't be afraid to show that you like her. Stand tall and don't listen to what they say. They'll stop bugging you once they see that you're not annoyed or afraid of them. ;)