I would have to say that the most
common misconception about
bisexuals (from the point of view of the
straight hetero) is that bisexuals are
sluts who will
literally screw anything. Even some bisexuals make a joke about "there's twice as much people to pick from!"
From the gay and lesbian folks that my wife and I know, I found this to be completely wrong. From my limited pool of friends who are bi, it seems that they are much more discriminating. While they are attracted to both sexes, they have had several long-term monogamous relationships. Having a wider range to choose from also means that they can take their time to narrow the field. Of course there are "loose" people who are bisexual, just like there are "loose" heteros. Most of the folks who I know are bi don't divulge their preferences until they're very comfortable with the friendship. With the folks who have told me they were bi, eight of the nine had to add that they were not sluts immediately after the word bisexual left their mouths. This is rather unfortunate, and it is another reason why some folks continue to hide themselves from the general public.