How do you deal with people who are unable to understand that they are wrong?

I stop taking seriously the claims they make. When they talk, I smile and nod then change the subject.

If they say, “Why are you dodging the issue? Why won’t you discuss the topic with me?”

Reply, “Because your debate skills are so legend I am afraid you will destroy me with your air-tight logic and Internet information. Let’s talk about dogs instead. Isn’t my dog cute?”