I never got the whole bisexual thing.
*shrugs* As a heterosexual male, I don't "get" homosexuality. I literally cannot imagine being sexually attracted to another man; it's just not something I experience.
That's okay. I'm sure a gay man may really imagine being attracted to a woman; it just may not something he experiences.
We don't have to "get" one-another's sexual orientation in order to accept them as real and legitimate states of being. We can all just accept one-another as different yet equal.
Like it or not, bisexuals are attracted to both sexes. It's not a choice, it's just who they are. Why pressure them to conform to other people's paradigms instead of letting them be themselves?Just pick a sex organ you want to play with and be done with it.
It's like the lady says: "Baby, I was born this way."

Not always and not exclusively.
People do not pick their sexual orientation.
Well, this is getting into the question of Essentialism vs. Constructionism. Is a sexual orientation a natural state, or is it a social construction? Etc.
And ultimately what that boils down to is that there are a lot of degrees and shades of grey. There are people who identify as straight but occasionally are attracted to/have sexual affairs with people of their own sex, and vice versa. Human sexuality is often a spectrum more than a clear division. I just made an essentialist argument earlier, because I do think that most bisexuals -- who face discrimination from both straights and gays -- are Born That Way. But I also think that's probably a bit of an oversimplification; there are bisexuals who are more attracted to the same sex, or more attracted to the opposite, even as they are attracted to both strongly and persistently.
The bottom line is: We shouldn't be pressuring people to fit into neat little boxes. So long as no one is violating anyone's rights, we should just let people be themselves, to find or construct the "box" that accurately reflects their own inner nature, that reflects that they were "Born This Way." And we shouldn't be discriminating on that basis.