1. Toilet Spiders - I have to flush the toilet every time before I sit down (I'm fine peeing) just in case there are any spiders hiding under the rim where the water comes out. I don't want to get bitten on the ass while I'm on the toilet.
2. Heaters - I have to constantly make sure (if I'm the last person to leave the house) that all of the heaters are switched off, the fridge is closed, the oven, grill (etc.) gas is off and the taps are not dipping. I also have to turn one of the handles and shake the doors back and forth to make sure that they will stay closed throughout the day. This usually takes me about ten minutes (and makes me late for various appointments) and every now and then I feel the urge to go back inside just to make sure that everything is safe. (This is probably more OCD than anything else)