I came across this phrase when I was reading a detective novel An Innocent Client by Scott Pratt.
A policeman found the dead body of a priest with his penis cut off and said this to himself.
"What'd you do to get yourself killed, Rev?" Lander said to the photo as he turned into the parking lot at the Purple Pig. "Dip the old wick in a vat of bad wax?"
I'm not Christian. And that makes it even confusing.
Thank you so much.