1. there is also no subject which should invite conversation within a mens room. ever. Men go to piss, and they piss alone and in silence.
2. sometimes it can't be helped, but generally a good rule.
and never, ever work your way into a conversation with a girl in which the words 'I weigh xx stone' will leave your mouth. this will, much like a black hole, suck you into a conversation from which there is no escape, and will invariably leave you crushed and decimated.