I was with a client recently working on a conversation which had snowballed into a thorough disagreement.  Like all tough conversations it had come out of the blue.  Having looked at it from different perspectives she felt that there was a good chance that it could kick off again and wanted to talk about handling strategies for the future that didn’t include avoiding the colleague ad infinitum…  She came up with phrases that held her ground but gave the other space to change tack. I later found this HBR article which also gave some more suggestions that you might find helpful.