What about the idea that they want to have threesomes? It seems that bisexuality and orgies are irrevocably linked in the minds of some people (perhaps thanks to porn). Just because they like both sexes, people seem to infer that they like both at once.

I dated a bisexual woman for almost two years and inevitably, whenever someone would find out she was bi, they would ask me if we ever had a threesome. When I replied, "No," I would always -- without fail -- be asked, "why?" This was not only offensive to my girlfriend, but me, because they intimated that I should "take advantage" of her "broader" sexuality. At least thats how they see it.

Ultimately, "straight" society seems to want to demonize and make deviants out of anyone who isn't straight. Not everyone, but society as a whole. Because, by creating this image, people can separate themselves from that which they do not understand.