Like most people, I have my lines in the sand, but I think they are based more on the thinking behind what people say than the thing itself, if that makes sense.
I don't have racist friends for instance, and can't imagine being able to connect with someone who could write off a large group of people 'just because'. I don't know if I could just agree not to talk about race and ignore it, though. People who think like that would let it show in other ways too, I think. It always leaks out somewhere, as it is rare for someone to be intolerant of one group and not of others - it's a mindset, really.
Having said that, I am very careful not to make assumptions about people's motives for saying things. I don't like people who think that anyone who disagrees with them is doing so out of bigotry, stupidity or ignorance, when actually they just disagree. Bigotry works both ways, and being closed off to different ideas is bigoted in itself, as well as being rather arrogant.