I know how you feel.. my mom has OCD (in my mind, as well.. she hasn't been diagnosed by a doctor) and she appears to be bipolar and she has a lot of psychological problems like depression..
I don't know that you can really do anything to keep it from angering you or making you sad.. i, too, feel bad for my mom and she does make me sooo mad sometimes. She makes me do crazy things to clean and well, it's not fun to live with.

But I love her to death, she is my mother. I think the only thing we can do is be there for her/him and accept them as they are.