Yes, many weekends at my in-laws' house. Many family members have opinions about many things that are not based on facts and reality. In these cases my action is not to take any because I've already done it and the result wasn't sociably good.

With third parties my attitude is: -Say nothing - let them stay stupid, I'm not a teacher of stupid people. -Explain that they're wrong in a polite and articulate way - if I care about their knowledge. Show them how dumb they are like a door - colleagues and close friends in general, since I care about their knowledge.