It's just like how people seem to think homophobic means "gay hater". I know some people believe that many who hate gays have deep issues with homosexuality stemming from a fear of it, but people seem to tend to use it out of the proper context a lot.
Also, I find that most people under the age of 22 or 23 who say they are bisexual are either attention whores, want to seem trendy, had a single homosexual experience/have just 'experimented', or are gay and don't want to admit it yet.