Not bisexual myself, but... Escapist-only info, being totally honest, I wondered if maybe I was. I concluded that I just don't have a cow when I see a man naked, but I'm only sexually and emotionally attracted to women... so I was straight, but secure in my sexuality.
Somewhat unrelated story aside, I can guess that it's very freeing to know you wouldn't mind it either way, but a little harrowing (as I imagine just being gay is as well) because people are even less likely to understand and not get creeped out by you. It's kind of depressing when I think of it that way. Like has already been said, it's different for everyone and not every bisexual fits neatly into an exact definition. Someone may identify themselves as bisexual, but only be attracted to under 10% of the otherwise attractive and interested girls they meet, or vice-versa. Asking someone to quantify and collapse their whole spectrum of sexuality into a neat little summary is asking a lot, and for a lot of people, asking the impossible.
To answer the second question, no, I don't believe someone can be "tricked" into having a different sexuality. That's what homophobes say when their children turn out to be gay... maybe it was that person they were hanging out with, maybe it's taught too early in school and confuses youngsters, it's just a state of mind, it's just a phase, etc. etc..... I have to wonder about the combination of those two questions. Is the OP trying to indirectly tell us a story from his own life?