Personally, I am polyamorous in this regard.
Because the bathroom is so honest, you must treat it like a drunk friend who knows too much: Be wary, for it will spill your secrets when you least expect it. Not out of malice, but simply because that is its nature. You may think you're putting your best foot forward and really charming the literal pants off of someone, and then they excuse themselves to use the bathroom, at which point you have zero seconds left to stem the tide of what may follow. Is there filth-encrusted tissue sitting on top of your trash can? How about errant feminine hygiene products? Is the bowl clean, or is it decorated with a thin layer of ass spackle? Has anyone pissed on the wall and left drip marks that shine in the light when you turn your head just so? Is there a hairy razor sitting on the side of the sink? Did you hang a wet pair of underwear over the shower rod? Is your hemorrhoid cream sitting out? THERE ARE SO MANY QUESTIONS!
The one-night stand is a purely impulsive decision based on your boner or lady boner's insistence that you rub your groin on someone else's until your brain nods in fervent agreement. Both of them, and you at this point, will have forgotten if you bothered to tidy up the house. You will only remember at the moment your new crotch-cuddler asks to use it, and at that point it's too late to do anything about it. A solid rule of thumb is to give your bathroom a once-over every time you leave it. Look at it as if you were visiting someone else's, and if anything makes you cringe, fix it before you leave.