I used to think leaving the toilet seat up was a major offense. When I was still living at home and woke up during the night to get a drink or go to the restroom, I didn't turn the lights on.
One night I fell into the toilet! It's not only gross (although my grandmother's toilets were always pretty immaculate). But, it's painful. You don't realize how soft a toilet seat is until you instead feel porcelain. Porcelain is very hard.
But, nowadays I turn the light on when I get up at night. And, I've learned to not mind the grandkids leaving the toilet seat up. It means that they did lift it instead of ...... all over the seat!