"what ARE naughty bits?"
That's easy; naughty bits are any bits you have fun with.

Truly spiritual Christians realize that it is inappropriate for a Christian to engage in any activity for the deliberate purpose of having fun.

Sarcasm aside, I knew one poor young man years ago who had actually set just that as a standard for himself; Even the very conservative Christians in his peer group tried to get through to him. I've known a few others who would never vocalize what he said, but who tend to act as if they believed it.