Based on 'You know you're an Irish Dancer if ... ' (post replies), I decided to make my own
Starting off with ....
YOU KNOW YOU'RE
So. You Know You're OCD if....?
...you stay behind after class to neaten all the exercise books
...if pens are in a pot and some of them are upside down, you will stop and turn them the right way up
...if something is off centre you will rewrite it all until it is
...if your alarm clock is a minute off you will hit it