I'm OCD about pretty much everything. I don't switch the lights on and off every time I leave a room, or wash my hands 8 times before I'm satisfied that they're clean, but everything has its place.
If it's moved even slightly, I'll notice. The front door needs to be checked twice to make sure it's locked and I list everything I'm taking out with me. No one else is allowed to use my cup, plate, knife, fork or spoon. If they do, I have to get new ones. This is always a problem if we eat out. With drinks, I solve the problem by using a straw, the food is a bit more problematic. I always put my clothes through the wash twice and they can't go in with other people's clothes. The bath/shower must be rinsed at least three times before I can go in. And I never, never sit down on a chair directly after someone else has got up, the sensation of someone else's body heat is just wrong.