I hope you don't mind me jumping in before Angie gets a chance.
When you mention guys at school being mean, I assume that you are pretty young. And I don't mean that in a bad way...or that you don't know your own mind. You obviously *do* know your own mind, which is wonderful. You just need a little more self confidence to stay true to your own style sensibilities.
For the most part, young men don't know squat about fashion, style, cut, proportion, or anything else. There are a few that do, but they aren't likely to make comments to you about how cool they think your hair looks. So I say to just ignore the comments from the mean boys. Some of them probably have secret crushes on you, but they are too scared to admit it, so they go along with the meanies just to save face.
If you truly wish to feminize your style to go along with your new potential haircut, there are ways to do it that won't compromise your basic tomboy style. And once you get your hair cut, you may feel like changing up your wardrobe anyway, just to keep the excitement of change rolling along.
I haven't been around the blog long enough to get a handle on more than a few of the other members' style preferences. But you may want to look at Rae. She has a short haircut and a tomboy style, but she can also look feminine and fantastic at the same time. You may be able to get some ideas from her.
http://youlookfab.com/member/rae/
Annagybe is another blogger who appears to have a tomboy base to her style, but with plenty of fashion forward touches. You may want to look at her posts and pics for some ideas. Her hair isn't pixy short, but her sense of style may be something that you can emulate to a degree.
http://youlookfab.com/welookfab/profile/annagybe
I know there are others, so look around. And I'm sure someone will comment later in this thread with more suggestions.
Honing your personal style takes time, so be patient. In the meantime, remember that school doesn't last forever. Before you know it, you will be in the world of adults, where you will have a little more freedom to pick and choose the people you spend time with. The people in your adult life will also be more mature, and hopefully more able to appreciate you for who you are. So hang in there. Be the best you that you can be, and know that the people who make fun of you are too shallow to find anything better to talk about with each other.