It's a difficult one to call. They ALL are. A lot of it is in the beholder. I use terms like "Paki shop" innocently enough (A shop owned and staffed by persons of Pakistani origin), but wouldn't actually call a Paki a Paki, unless we were friends....PFFT YEAH LIKE I'D EVER BE FRIENDS WITH ONE OF "THEM"!
Point is, certain sections of people seem to take more offense at things than others. A Paki would more than likely be offended if you called him a Paki, no matter how innocent it was, but if a Scots person got called a Jock, chances are they wouldn't mind, unless they were a knuckle dragger that had those kinds of "problems", they unfortunately do exist here...