I think everyone is on some sort of broad spectrum regarding sexuality. We have the capacity to be pan sexual or bisexual at least, but social pressure and other such environmental factors can inhibit people from 'batting for the other team'. Those who tell me they are straight as straight can be have demonstrated the opposite; I have walked in on enough of them.... or the next week, she jumped me when I went to her house to accompany her on piano.
I unthinking most people lean more to the straight side, but might wantfool around with the same sex if drunk or otherwise less self censoring/self conscious. That's what I've seen anyway. Also, you might be attracted to the same sex but not act upon it. I have heard other bisexuals joke about becoming lesbian/ gay or straight for a while if one gender realy pisses them off, and to an extent I think some of us do 'switch off' temporarily from one gender or tend to have a preference.. Which lead me to ask straight friends if they know they are straight. Most admitted they had just never thought about getting with the same gender and wouldn't be averted to trying it.
I haven't been with a girl in a few years but then again I could never approach anyone anyway. In fact, I was turned down by a girl who claimed she was straight and 2 weeks later was the first time Isaw her outed... caught in a bathroom stall with another girl who turned me down the year before.
Right now, I would still appreciate female company though Tip Top wouldn't take kindly to it. We joke about the hot waitresses he sees at work. Not all bisexuals are like this, but I believe myself to be genuinely polyamorous. I think a lot of people are kidding themselves about that as well as gender preference, but it is NOT the same as just being ready to fuck everything and anyone.
I mean (men) if you were(willingly) blindfolded and a guy was all up on you instead of a girl, would you tell the difference. It might feel pretty nice I you get past the mental block, but to be fair, you could argue the difference is like the difference between a consensual sexual encounter and a stranger/family member/creepy ugly old man raping you...that disgust factor could still be the same I guess.
Personally I can't envision 'writing off'an entire gender, or telling someone you are not into them because of their sex, the same way I couldn't do that because of the colour of their skin. I love a person for who they are, not their genetalia.