Generally I get on fine with my Dad, but I'm glad I don't live with him any more. Sometimes when I am staying with him for a day or two it reminds me how difficult it could be, he is a bit of a grumpy old man at times (perhaps understandable as unfortunately we lost both my mum and sister to cancer).
Basically he has quite a harsh tone of voice when something is annoying him, and everything has to be done in a particular way, even mundane chores like hanging up the washing, if it isn't done just right then it feels like he is chastising you.
He is also very fussy about technology, when we got him a PVR as a present it was quite a hardship teaching him to use it, you had to explain every last detail to him, even the stuff that is very intuitive to most people like how to navigate menus and such. He'd get frustrated if he felt I was going through things too quickly and the same goes for computers, he likes everything in a certain way which sometimes then causes issues. For example he has a narrow (5:4) monitor and yet insists of having a favourites bar on the left side of the screen, which effectively shrinks the browser aspect even more. This means that some websites may not really display optimally.
Things like Christmas probably another good example, generally not a happy time of year for us, he gets stressed out easily worrying about getting everything ready and barks out orders. My dream is to one year have Christmas in my own house.
Of course I love him, and generally since moving out 5 years ago things are fine, I've been a lot less stressed in general and it means meeting up with him is a pleasure rather than worrying about getting 'told off' for something.