Great mates

So my friend Ass and I have decided to find each other a partner. In fact, there's a wager going on as to who will find the other a partner first. It didn't start well when she jokingly tried to construct a personals ad for me, calling me a mathematician.

For the record, the personal I would write for myself would be:
"Low maintenance, non-smoking, eco-friendly girl seeks male version for gigs, card games and adventures on foot."

ANYWAY, I don't know what it is about me or my body language that doesn't quite communicate the fact that I understand when someone is joking and often return the joke, but the return joke isn't accepted as being evidence that I understood the original joke.

So Ass has her mathematician joke.

I return with: "I'm not sure I want in on this any more, I don't think you'll accurately represent me."

A genuine protest: "I'm joking!"

Now, Ass and I have been friends for more than 12 years. In the absence of a need to have a best friend, she would be one of the closest relationships to a best friend I have. You would think by now she would know when I understand a joke and turn it back.

Is it because I played it serious? Is that the cause of confusion? But surely someone who knows me well would know my deadpan mode. Or am I really just not as well known or understood by my friends as I at first thought? Maybe I'm not such an open book.