To be honest, I'm not at all sure the flirting is related to bisexuality perse. Straight women, knowing each other to be straight, can still flirt with each other in a sexual way, in my experience. So yeah, lots of us identify as bi (me too if you were wondering, and you probably weren't) but that might not really be the point with the flirting, necessarily. Which doesn't mean you should feel obliged to, because obviously some people are flirtier than others and that's okay. In my not-so-humble-in-this-case opinion anyway. :)