The "me too" movement has educated many about sexual harassment. But this is not just a movement. "Me too" is a rule of evidence.
Most people have heard the term "character evidence." Character evidence is evidence about a person, such as that the person is generally has a trait, such as a "good" or "bad" person. Generally, evidence that a person has a certain trait or usually acts a certain way, can't be admitted in a jury trial to prove that they acted that way on a particular occasion. For example, that a person usually grocery shopped on Saturday generally is not admissible to prove that they shopped on a particular Saturday at issue in a trial.
In the context of a sexual harassment trial, this same concept has been used to excude evidence that the harasser sexually harassed other women. By excluding this evidence, the harasser can claim that they did not harass the victim in the case or that they thought the victim enjoyed the banter, etc. Essentially, it makes a case harder to prove by giving the false impression that the victim at trial is the only victim of this harasser. Excluding this evidence even allows a harasser to falsely deny that they harassed other women, knowing that the court won't allow those women to testify and prove them a liar.
Thankfully, California courts have remedied this injustice. Courts allow "me too" evidence. A good discussion of why this evidence is admissible can be found in the case Pantoja v. Anton (2011) 198 Cal.App.4th 87.