I have a personal rule, and I don't know where it came from, but it's: No outside things can touch the inside of the bed.
For example, if I want to put a bag on the bed, I would put it on top of the duvet. Absolutely no way in hell could I put it on the bottom sheet, or if the duvet was rucked up or folded over on the inside of the duvet. It makes me on edge just thinking about it.
Please share your weird personal rules (lighthearted + no judgement here)!