The spread of STD's is a result of not having any societal shame or ridicule for sleeping around.
Listen to yourself; shame, ridicule. All negitive methods, with no positive ideas.
Explaining the possible consequences of a person's action in a more constuctive way would be a much way to go about it.
Hey, lighten up. I was just joking. Look at my comments, I said, JUST KIDDING!
Sometimes the stick works better than the carrot. Look, screwing around is FUN, no doubt about that, but the consequences seen and unseen to you and those around you are in many cases permanent or fatal.
The problem is that most people don't think about the consequences of their actions. And in the absence of their thinking we should all tell them that what they are doing is stupid.