6.If you play with your privates too much, they'll drop off/you'll go blind.
Your parents want you to emulate the Seinfeld episode and become master of your own domain. Its not sure if this lie is as common now with parents as it was way back when, but most parents would prefer that their little ones not sit around "discovering" their privates in public. And most parents also don't want to risk walking in on Johnny playing with his Johnson in his bedroom. So this lie is most likely still in widespread use.