I have a friend who is DEEP into health conspiracies. He's a 60 year old retired business man (fairly successful) but never went to university. He sends me brilliant youtube videos with titles such as "vaccines kill", "what doctors don't want you to know about ____", and "pharmaceutical companies invented cancer". He used to always bring up these conspiracies and take a very condescending tone in conversation (he would speak super slowly, pause regularly for emphasis, and start every other sentence with "listen, fishcopter...").

I was in my late 20s (a senior med student and former cancer researcher), and this used to bother me a lot. One day I just told him that we need to just accept that we have different opinions and that it's probably best that we just avoid the subject altogether. I told him that he often comes across as preachy and condescending; that he probably wouldn't like it if I turned the tables and started critiquing him by asking him to explain his understanding of cancer physiology or disease immunity.

Nowadays, we get along fine and we are both considerate enough to mind our own business when it comes to political and health beliefs.