Generally speaking, Paul has never once walked off to take a piss without me noticing. The lack of movement means I would wind up killing his ass and teabagging it for trouts and giggles.
Back in the day, I used to do split screen multi-player all the time. Those were some funny nights, me a few mates, a case of beer and progressively worse gameplay from all of us. Though I fondly remember one shot weapons on Medal Of Honor Pacific and abusing the spawning locations to repeatedly spawn kill a person in what truly became the first time I can say I spent time with a friend "competing for a spawn kill" though not the last by any measure
These days, I prefer to play online, this way if I need a piss and Paul is ranting about how much he wants to lick a pony or something I can gently put my headset down and go for a piss and because I'm generally trout at games he's oblivious to the fact.