I hate when someone says something incorrect, and when corrected they huff, "Are you calling me a liar?"
Most of the time the person asked that question becomes embarrassed and apologetic saying, "Oh no, of course not..."
Instead, I just say, "No, I'm calling you misinformed. But if you choose to propagate this misinformation further now that you know it's incorrect, then you will be a liar."
Unfortunately, they probably won't admit that they're misinformed, and they'll cite web sites and propaganda to try to show you they're right.