For example - I'll ask her what she wants, and she'll tell me she doesn't know.
My experience of geek girls is that they only say that when it's absolutely true - and it's very clear that it is, and it distresses them that they don't know.
My response was "Ah! Yes! You grok!"
Because it absolutely does distress me to not know my own mind - and I've seen this in a few other geeks as well...