All women are bisexual, please read first because it's not what you think?

Okay I know that this is very false so I'm not trying to promote this idea. But, why is this such a common question on this forum? Is this from guys in the club/party scene that witness this behavior? Or is this from a lesbian that has wishful thinking? Also, how common is this opinion of all women in real life? Because on other forums or amongst my group of friends I've only heard this once, and the guy was just playing around wanting the get the girl offended from what he told me. Do that many people really think this?