So this has happened a few of times recently, I start talking to usually a more introverted girl and she starts getting defensive about meeting me (a random guy).

The conversation will progress and we'll start talking about, for example, our careers, I'll say something like, 'I'm a student, I study this awesome subject called computer science'. Obviously there is a bit of self mockery here, but sometimes girls I talk to will grasp on that and the conversation from there will basically just be her trying to act like she's a cool smart ass bitch, "ohh that's so lame" etc.

What's the best form of defence? Join in with a bit of self mockery, or get defensive? Maybe something inbetween? Maybe I shouldn't even be in this position to start with, what can I do to stop it happening again?

Thnkz