That's right, you heard it here. Do not, under any circumstances, be you man or woman, conduct any business in the bathroom. At best, participants will be distracted. More likely, they will be so busy trying to ignore you and focus on the task at hand that it's an awkward waste of time. At worst, you are going to offend some client and blow that multi-million dollar deal. So leave the business to the boardroom and/or golf course.
Rule the Second: Wash Your Hands
You know what's worse than seeing some stranger in a public bathroom leave without washing their hands? Seeing somebody you work with do the same. Because now you get to spend the whole day wondering what they are touching with their filthy, disgusting, germ-ridden hands, and hoping it's not on your desk. I really don't know why we have to keep talking about this rule, but given the number of socially inept non-washers I see at work on a day-to-day basis people still aren't getting the message.
Rule the Third: Don't Lie in Wait
Okay, so you need to do a #2. In some cases, you might stand around a full bathroom waiting for a stall to open up, but at work you shouldn't. Nobody likes to feel pressured, so give your coworkers some space, go back to your desk, and try again later (or try another bathroom). Even if the person currently doing their business isn't aware of your presence, they are still going to feel awkward when they come out of the stall and realize you've been timing just how long they've been in there. So save them the embarrassment.
Rule the Fourth: Everyone is Equal in the Eyes of the Bathroom
So you're the boss. Maybe you're even the boss' boss. Doesn't matter a whit in the bathroom, you've still got to follow the rules. Don't start up any business, don't expect to cut to the head of any lines, and for goodness sakes yes you do have to wash your hands or flush. Being numero uno doesn't give you any special privileges whatsoever.
Rule the Fifth: Keep Down the Stink
Your bathroom at home probably has a fan, and I bet you put it to good use. Your bathroom at work probably doesn't though, which means that everybody else in there with you and after you can smell what's going on. If you think it might be an especially stinky trip, consider a courtesy flush. People will thank you.
Special Tip: Dealing with those who Outrank you
Maybe your boss was clever, came here, read these rules and is acting like he should in the bathroom. Then again, maybe he's not. Maybe he keeps trying to strike up a conversation with you at the urinal, while all your instincts tell you to stare straight ahead and ignore them. I feel the need to warn you that following proper bathroom etiquette rules in the context of such an ignorant boss may jeopardize your job, or at least your standing. Yeah, it sucks but the boss might not care if you are ignoring him because you are in the middle of taking a pee, all he knows is you are ignoring him. So try to strike a healthy balance, don't tell him to "piss off!" (clever pun!), but don't linger and chat either.