My roommate only washes up if he poops, never after peeing. Now every time I’m in any of the common areas I have to wash my hands after touching anything I haven’t wiped down. Thus, I wash my hands twice every time I use the bathroom; once as normal and again in the kitchen because I touched the taps, light switch and door handle in the bathroom which likely have groin sweat on them… /rant
I had someone suggest this to me once. His logic was that he knows where his dick has been and showers daily.
I subsequently came across a “Straight Dope” article that debunked it. It’s best to wash after.