"There are two kinds of men. Those with dirty cocks, so when they go for a piss, they have to wash their hands afterwards to clean them. And those with clean cocks, so when they go for a piss, they wash their hands before hand so as not to dirty it." Détective; Jean-Luc Godard

Apply that to shitting, and you get the idea. Would you shake hands with a guy who's just been for a shit and didn't wash his hands? I wouldn't. And so I wouldn't like to sit down on a seat he's just sat on to shit in either.

That final sentence was fantastic. Read it again.