I am obsessed with symmetry. If I scratch, say, the left side of my face, I have to scratch the exact opposite spot on the right side of my face with the same amount of pressure, friction etc. If I get the wrong spot, I have to balance that on the other side as well. This has the potential to occupy me for several minutes. I've tried 'not' scratching/poking the opposite side and it drove me to absolute distraction.
In any conversation, no matter how (in)appropriate, if someone says "two weeks", I involuntarily start saying "two weeks" as well, maybe two or three times, in a way that's similar to the customs scene in Total Recall. My sister has the same problem, apparently.
When I talk to people about places and locations, I invariably end up physically pointing in the direction of where ever I'm talking about.