Common in futuristic settings, free-love or otherwise, where the more enlightened future humans have outgrown such silly hangups as caring what sex their partners are (and in some works, what species), even if their society hasn't yet embraced extreme promiscuity.
While it's not Truth in Television, it truer than people often think.
Contrast Suddenly Sexuality, where a character skips from gay to straight or vice versa with no warning, and No Bisexuals, where the characters/narrative don't consider bisexuality as an option.
Compare Casual Kink, which is the same thing for BDSM and fetishism.
Bisexuals are not portrayed so much for their mannerisms as their supposed habits.
As a result, a het-seeming bisexual reads as Straight Gay, whereas a bisexual that acts Camp Gay is likely to be seen as subverting the stereotypes associated with a camp persona.
It'll help you get more interest from our horny members.This site is not pornographic, it's simply a meeting point for like-minded and open-minded bi singles struggling with their feelings.With over a million topics and posts, and thousands of members, our community is very attractive and has been bisexual online dating business since 2001！ It's definately not all serious stuff though.Compare If It's You, It's Okay, where someone who has shown interest in people of the opposite sex in the past has exception.Contrast Depraved Bisexual, where bisexuality is used as a way to make the character seem more evil (or conversely, being bisexual makes you evil), and Anything That Moves, where bisexuality is treated as a lack of discrimination in partners (in real life the two are not necessarily linked; just as straight and gay people don't find of their preferred sex attractive, bisexual people don't find "everyone" attractive).