Depends on who I'm talking too really. My dad's side came from Newton Heath and he was the only blue in the family. I had 2 uncles who were reds and cousins who are. Can't really go calling them rags or scum but friendly banter has always been fine. Same goes for several friends who are reds.
However, if I'm taking to out of town TV rags trying to belittle me and my club i don't hold back. I've managed to put most in their place in pubs up and down the country. The ones who go to OT and know their stuff I can talk to, other's soon get told to do one if they are being disrespectful.