Hmmm, I've got a few.
I have kids... as well as a bunch of younger siblings, so you would think this wouldn't bother me. Ahem, I can't stand seeing small things spilled on the floor. If they're big I don't care, but stuff like mega blocks or cheerios I clean up the second I see them hit the ground. I can't stand it...
Uhmmmm, I am constantly cleaning the surfaces in the bathroom (counter, tub ledge, mirror, doorknob), even if I only cleaned them the day before and they don't look the least bit dirty.
In the kitchen I have two. I can't stand to see a sponge/washcloth sitting in the sink. It has to be thoroughly rinsed, wrung out, and sitting neatly by the tap. Also, I hate it when dishes are not stacked in a certain way.