What is the thought behind the common notion that to be bisexual means that you are a slut?

I hear this far too commonly and never understand why people think this.

Some things I’ve been told: if you’re bisexual you have to sleep with both men AND women to be satisfied, which is why a bisexual is bound to cheat on their S.O.! You have to sleep with a man and a woman at the same TIME to be satisfied if you’re bisexual! Bisexuals are people who love sex so much that they can’t restrict themselves to sleeping with people of only one gender! (The list goes on…)

So where are these ideas coming from? Does anyone here think this, or did anyone used to think this, and why?