Girls, what would be your motivation for constantly teasing a guy?

I have noticed that this classmate of mine teases me (playfully) a lot. Actually we do it to each other and most of the time we are arguing and calling each other names. Although her personality is being a bit of a smart ass, she doesn't really tease other classmates this much. Even if they tease her, she laughs with them and just takes the joke but when its just us we have this constant battle and go back and forth for the longest time and sometimes people will tease us about it and how we act like little kids (one time our teacher jokingly told us that we needed to learn to work together). If I ask her why is she being "mean", she just tells me I'll get over it or that she does it because I'm annoying. One day I decided to not talk to her (at least the way we usually do) and just kind of ignore her. As soon as she saw me that day, she looked right into my eyes and had this big smile on her face and said hi (when I usually get a very dry greeting, or sometimes none at all and I have to remind her). Sometimes it bugs me because she seems so at ease with other people and even though she smiles a lot when we talk, the fact that she calls me annoying bugs me a bit. Is the constant teasing a "good" sign and her way of flirting? or should I just take her words seriously and leave her alone?
Girls, what would be your motivation for constantly teasing a guy?
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