In school, with most girls I talk to, I'm not trying to start anything romantic or sexual, it's just casual chat. However, my chat tends to always be about school-related things or mundane things, and I don't have any girls talking to me interestedly because I don't have the reputation of being an open to sex/dating sort of person. Rather, I'm just known as the smart guy.

How do I go about changing that? I don't want to outright flirt with girls unless I'm actually interested in them, I just want to have conversations but these conversations always get so formal and non-friendlike.