My brother has a good anecdote which doesn't involve toilets per se but it does involve a penis and sudden violence, so it sort of belongs here.
He was on a business trip to some hilly coastal resort town in the Med somewhere (this is relevant, read on). He'd had dinner with his clients and business partners and was walking back down this little steep winding road towards his hotel, when he turned a corner and found himself face to face with a man, a complete stranger, who immediately dropped his pants and started masturbating furiously. (I'm going to assume he was doing it furiously - it's not really the sort of situation where you'd pleasure yourself languidly. That would be totally inappropriate.) So my brother reacted with some sort of lizard-brain by-passing of his higher functions by walloping this guy in the face as hard as he could (he's not a trained pugilist but he's fairly stocky, so there's a good chance he broke the guy's nose) and legging it back the way he came.
After a couple of turns on this little road, he paused and looked down and saw the man stumbling along with his pants around his knees, trying to pull them up with one hand while cradling his profusely bleeding nose with the other, rapidly detumescing* cock still visible.
*second outing in the thread for this excellent phrase