Fair enough. I see your point that people do tend to fit into straight / bi / gay categories, but what I am saying is that those categories are too narrow to fully encompass the full spectrum of human sexuality. While those categories are certainly very USEFUL to help us more easily identify sexual orientation, and MANY people do fit neatly into them, they are unhelpful in certain circumstances where there isn't a good fit.
Perfect example is me. I'm not exactly bi, not exactly straight. "Mostly straight" is probably the best description, but you're not giving me that option, so I just say "straight" to keep things simple even though it's not really 100% accurate. But what happens if we are out at a rave and I make out with a dude? Am I gay? Bi? No, I'm mostly straight still. My orientation hasn't changed, but your perception has. And now you've stuffed me into "bi" when that's not really an accurate description.
In the case of the original poster (or whoever it was that had someone kiss their hand), their friend may be similar to me. The compulsive need to categorize people into one of those three groups blinds us from the ability to accept that they aren't exactly ANY of those three choices, and by virtue of categorizing, we make certain assumptions about who they are. For example, the assumption that I'm bi if I were to make out with another man would be wildly inaccurate, just as the assumption that a girl who makes out with another girl is bi or a lesbian could be wildly inaccurate.
In the end, I think we are both right in our own ways: Yes, categories of sexual orientation are useful in certain contexts and help us to make decisions and understand our world, but when it comes to interpersonal relationships with our friends, I don't think they're terribly useful, especially when rolling balls.
If you let go of your need to categorize people (whether it's sexual orientation, social status, level of education, or race) you'll find you get to know people more completely and truthfully for who they REALLY are, not for how you've categorized them.
And to me, that's what rolling is all about in the first place.