If a female colleague sexually harrasses a male colleague at work, is it ok for him to do the same to her?

Why would you lower yourself to enter into the same playpen they use? You need to be professional, so dreaming up ways to get back at these women is not appropriate and is not going to be beneficial for you in any way. Now you need to write down all the incidents you remember and any subsequent ones, noting times and dates and what specifically the acts were, then you need to go to HR and file a grievance for sexual harassment and creating a toxic environment for you in the workplace. In the meantime, keep doing the right thing by totally ignoring them. If HR does not resolve the problem you can sue them because that is actually illegal. You might also want to consider another job.