Ha, toilets. Yes, I check before using. *Usually* I check for toilet paper in public restrooms before using. If there's a lid, it goes down when I'm done (to protect the bathroom from tiny droplets of spray). And if I'm at my parent's house, I then put it back to my mom's favorite default setting (seat down, lid up). At other people's houses, I put it back the way I found it unless it's a party in which case I leave the seat and lid down.

And keys. I'll always remember the time C. closed the locked door to his car and then immediately said, "Whose got the keys?" Yes, they were still in the ignition.