I had this conversation with a guy I know very well, and his stupid rationale was that a penis is just a body part like an arm. And according to him, I would not wash my hands if I touched my arm under its sleeve. I reminded him that my arm does not lead to urination, and butts have skin too. After shaming the shit out of him about it, he has been meticulously washing his hands ever since. I am still annoyed I had to have this conversation with a grown man.