Shit i don't like - electrical plug switch on, nothing in the socket.
This drives my OCD bloody crazy.
If I see an electrical switch left on, with nothing plugged into the socket it is attached to, I will actually drop what I'm doing and cross the room to turn it off.
I've been laughed at and stared at blankly like I'm some mythical creature when I do it, but I don't care. It just bothers me to no end when I see it.