There outta be a law...
I've heard my mother utter that phrase more times than I can count over things like motorcyclists riding without helmets (there are laws in some states mandating helmets, you know), little kids being let out of the house unkempt and with crusted food all over their faces and paws, and so on, and so forth.
Yet, every one of those behavioral issues that prompt us to say "there outta be a law" is about common sense. It's stuff that people with IQs above 12 should know.
Anyway, if you don't believe me, drop your jaw, read this story, and tell me if you really think we need a law to prove the behavior in question is down right crazy, just plain wrong and bad, and outright nasty, unless you're a farm animal...literally.
CLARIFICATION: Jay's comment made me realize that some folks might think I believe we don't need laws to manage bad behavior. We do. I'm just saying that some bad behavior shouldn't require a law against it, before people realize they shouldn't engage in it.