Random Thoughts on Conversations

I occasionally "office" in public places which subjects me to the public. Quite often. I overhear a few racy conversations and I never know what to do. I sit there thinking, they must know that I can hear everything...why would they talk about this in a public venue? Sometimes, these conversations involve middle school aged children. I volunteer with kids in this age group so I'm always torn wondering if I should say something. I never do...