three reasons why the concept of “fake bi girls” is bullshit and people who come out with these stories about “oh i saw two girls kissing in public to get a guy’s attention, fake bi girls ruin everything for everyone!” need to sit down:
one—nine times out of ten the “fake bi girl” y’all are talking about is a complete stranger who you don’t know from adam and whose sexuality you’re assuming based on nothing more than appearances + biphobic stereotypes, assuming that if someone “looks like a party girl” they can’t be bi or their bisexuality is fake or that two women kissing in the presence of a man could not possibly ever be “actually bi”.
which goes to two—i have literally never seen the issue with two women kissing in front of a dude (as long as they’re not being pressured into it and are doing it of their own consent), whether they’re bi or not. maybe they’re bi and he’s a friend who they’re hanging out with, maybe they’re bi and in a poly relationship with him, maybe they’re bi and in an open relationship, maybe they’re bi and have a voyeurism kink, maybe they’re not bi and yet they’re still two adults who are allowed to make their own sexual choices and kiss whoever they want whyever they want and it’s no one else’s business. the whole “you kissed in front of a man? EWW” thing reeks of sex shaming and the kind of biphobic nonsense bi women have to face constantly over being attracted to/involved with men, that there is something inherently “gross” or “dirty” about being with men or doing anything sexual with them.
and three—random women who may or may not be bi making out with each other is not the root or even a major source of biphobia in the world. someone who is biphobic and refuses to believe that bisexuality is real isn’t doing that because they saw two girls kissing in a club in vague proximity to a guy one time, and if they say that that’s the reason then they’re only using it as an excuse. there are stereotypes of every marginalized group and there are always people who ‘fit’ those stereotypes to some degree, but they are not at fault for the oppression and discrimination that group faces and them living their life as they want and being themselves is not to blame for people who use stereotypes about their group to delegitimize and deny them.
ultimately the concept of the “fake bi girl” is built on sexism and biphobia, assuming the orientations of random strangers and refusing to consider them to be bi if they’re not a Good Bi who lives to break stereotypes (something that is harmful particularly towards polyam bisexuals), and sex shaming people for the consensual sexual choices they’re making.