Which is the best method of avoiding peer pressure to enage in inappropriate sexual activity?

You're in the breakroom at work when you see a coworker posting a cartoon on the bulletin board. you read it as you pass, and it's a joke about women breastfeeding in public. a male walks up, looks at it and starts laughing. other make employees walk up, and one takes it down saying he is going to make copies for everyone. what do you do?