Someone I used to work with has OCD. She would constantly wash her hands until it bleeds. Her desk had a certain way for everything. It would take her about 20 mins to leave work because she double checks everything, she would pick up the phone to hear and dialling tone, put it down to make sure it's down properly but only to pick it up to check it was down properly...after that, she would open and locks her drawers to check she has locked them. After 20mins of that, she would pack her bags, you can see her count out loud of the things she needs to do before she leaves and when she manages to leave her desk, half way out the door. More often than not she heads back to check again....
It was painful to see.