Asking how often the top blankets get washed
People always think they want to know. You don't.
No matter where you're staying, the housekeeping staff likely doesn't make anything close to what they deserve for washing sheets and bathroom fixtures caked in your bodily fluids. But for whatever reason, you're infinitely more likely to throw a couple of dollars to the person pouring your pint at the bar downstairs than the person cleaning your toilet later.
I'm not sure when or why tipping the housekeepers went out of fashion, but chances are, their salary wasn't increased to reflect the change. So think about setting aside a couple of bucks a day for the staff. To be extra cool, leave those dollars out daily, rather than all at the end of your stay, since the same person probably isn't cleaning up after you the whole time.
Using anything but a toilet as your toilet
Did you know that some people do their deuces in the shower? If not, I'm sorry to be the one to let you in on that horrifying human behavior. Shower, bathtub, sheets, curtains (seriously, WHY THE CURTAINS?), if it exists, someone will want to smear their business there. You would never be that person, of course! But someone, somewhere, is. And just guess what kind of tip they leave.