Thinking that things, inanimate objects, have thoughts and feelings of their own. It causes me problems. I can write about it here, about how pathetic it makes me feel, but when I'm in certain situations the thoughts are very real. I can't throw many things out because of it.
Having to do, or repeat things in my head, X number of times, usually three or five. Also having to do two or more things an equal number of times - if I do this three times, I have to do that three times. If I do it four times by mistake, I have to make it five, and then I have to do the first thing another two times.
Minor tidiness things too. I arranged the books on the shelf last week. It looks tidy but now I can't take a book out, because that would "ruin" it. I like to read at night, but I don't have many books lying around that aren't on that shelf.