I have pretty bad OCD - I don't hand-wash or have the repeated rituals that most people associate with OCD; mine is all in my head.
I count letters in words as I hear, speak or read them, and I have to make an even number of letters before I stop ... or a 9 letter word means I can stop as well. Until the next page, or the next paragraph or whenever, and it all starts again. It can take hours just to read one page when it's at it's worst.
I have to do things equally on both sides - footsteps, or if I catch my hand on the desk or clash my teeth together on one side, for instance, I have to even it out on the other. Sometimes I can sit for ages just trying to get the two sides absolutely equal.
I do things which are a bit like an extension of not stepping on the cracks in pavements ... although I'm happy enough to step on cracks, so I'm not completely barking! If there is a paved section of footpath between non-paved sections, I have to start with my left foot and end on my right - same with steps, start with the left, end with the right, nifty little shuffle half way down if I can see I've got it wrong.
Even dh doesn't know about any of this; he would think I was crazy if he knew. I did get as far as telling the GP when I was being treated for depression, but he didn't really take the OCD all that seriously because it wasn't manifesting itself in a physical way. He thought that the ads would help the OCD because he felt it was based in anxiety - but they didn't.