A Simple Literacy Test
It's often said that, because they can't be bothered to check for the seat before they sit down, women need to train their men to put down the toilet seat.
I've had the experience of nearly falling into the toilet when I've gotten up in the middle of the night to use the toilet, while too disorented and blurry-eyed to walk straight, but I still have zero sympathy for people who without even a glance expect the seat to always be ready for receiving their bottoms.
Rather, everybody needs to be taught to put the lid down. A toilet seat won't prevent things from falling into the toilet, like a hairbrush, a toothbrush, or a plugged-in curling iron (or even the cat).
Putting the lid down also reduces the incidents of small children flushing important or bulky, drain-clogging objects down the toilet. If your dog drinking out of the toilet grosses you out, just put down the damn lid!
Anyway, my household is good at putting the lid down most of the time, but many of my guests are not. It's annoyed me so much that I made a laminated sign stating, "PUT LID DOWN," complete with three downward-pointing arrows, and attached it to the underside of my toilet lid. Certain visitors still don't put the lid down, making me question their competence in literacy.