General advice:

• Be reluctant to talk about things you're not very familiar with.
• Double-check everything you say. Ask yourself how you know that it's true.
• If you want to avoid being factually wrong, just conduct yourself like you're on the stand in a trial: you pretty much can only relate things you have personally experienced, and you have to say "I don't know" pretty much all of the time if the discussion is about anything other than your personal experiences.  But you can maybe kind-of get around this limit by relating statements you read/heard by other people, for example saying "I don't know for sure, but I read an article by X in which he seemed to say Y".
• If you find yourself getting emotional, try to get away from that situation to calm down so you don't end up saying/doing something you regret.

Helpful resources

• Charlie Munger - The Psychology of Human Misjudgement.pdf

Specific mistakes:
 These are embarrassing to think about! I'm listing them because it was so painful to realize I was wrong in these cases that I never want similar mistakes to happen again.

• 2001-2005 - I should have been more aggressive / proactive in HS about taking care of things that were making me unhappy (acne, dating)
  • The acne thing is tough because there wasn't as much information out there on the internet about acne back then.  This was before Google Scholar, before YouTube, when Google itself was a new thing and I was still becoming familiar with doing Google searches.  But there probably were blogs out there that suggested switching one's diet.  I don't remember really focusing hard on trying to find a solution, probably because I was under the impression from the people around me that acne was a normal/unavoidable part of growing up.
• 2004 - When the movie "Troy" came out, I was in English class and criticized some aspects of the movie that I thought weren't in-line with the original work (which I wasn't very familiar with), and my teacher brought up that those were actually things that had happened in the books. (For example, the outlandish behavior of Achilles).
• 2004(?) - This one's really embarrassing to think about: while in high school I was thinking about South Park and was convinced(?) there was a hidden joke that, in hindsight, clearly was not there.
  • • Be aware that random chance can produce patterns that may look like they were arranged by another person, but in fact are just coincidences. This "finding patterns" behavior has also burned me with women.
• 2007 - A friend of mine recommended I should check out 'There Will Be Blood' and I assumed it was because the movie was about oil and that person was always talking about how the invasion of Iraq was all about oil.
  • Solution: Do extra research before using strong words with someone.
  • Solution: If you find yourself getting emotional, try to get away from that situation to calm down so you don't end up saying/doing something you regret.
• 2008 - I should have asked a lady I was somewhat acquainted with for an introduction to a lady I wanted to get to know.
  • Solution: ...don't be afraid to ask for an introduction? [Later: reach out to people! Talk to people if you think they can help you!]
• 2009 - While at Emily's birthday in NYC I blurted out, "Wow, you're really tall" when I turned and saw our transgender waitress next to us, which hurt her feelings / upset her (she responded sarcastically, "And you're very observant."
  • General things to watch out for in the future:
    • People can feel self-conscious about physical differences because they worry that others will see them as being less desirable because of those differences, or that people are evaluating them based on those characteristics rather than other characteristics that the person would prefer to be evaluated on.
    • People can get annoyed at hearing the same comments over and over (possibly even if they're positive comments).
• 2014 - While working for Edwina I was dismissive of the idea of Edwina using long, complicated passwords.  I don't remember what I said but it seemed to upset Johnny.
  • Solution: Be more cautious in giving opinions on things you aren't an expert about. (This is a tough one to fix because it came up in relaxed conversation. The best bet may be to just keep reminding yourself about this and hopefully the next time you're in a situation like this you'll remember what happened here.)
  • On the other hand, I do think that using unique, long, complicated passwords for every website is only feasible if you have a password manager.  Edwina didn't have one.  So in that kind of situation it might be a better idea to use an XKCD-style password.  But that was before I knew about XKCD.
• 2014 - In a random conversation I got into at a Starbucks, I confidently told the person I was talking to that "TED" talks were named that because they were started by Ted Turner, which is totally wrong.
  • I still feel embarrassed about this.
  • Solution: Double-check everything you say. Ask yourself how you know that it's true.
  • Solution: Be reluctant to talk about things you're not very familiar with.
  • Solution: You pretty much always want to prepend what you say with, "It's my understanding that (...)".
• 2015 - I knowingly implied something untrue in the wording of an email blast to professors.  I don't even remember what it was; IIRC it was tame compared to a lot of sales emails.  But IIRC one of the people contacted ended up upset about it.
  • Solution: Don't imply things that are untrue.
• 2016.11.24 - Dev offered me his book "The Quest", said he'd gotten it from a partner at S, and I was skeptical that it was any good, saying that no one would offer someone else an autographed copy of a book they had a very high opinion of. But later I looked it up on Amazon and it actually looked like it was a really good book.
• 2018 - I saw a cat over the course of a few months, and thought he was OK and not hungry because someone else was feeding him, but the cat disappeared one day and it later turned out it died. I think my mistake was to not recognize its lack of appetite as a potential serious problem. I also didn't spot its weak hind legs and yellow gums until the last time I saw him, and it didn't occur to me that it might have a serious health problem until I saw how weak he was the last time I saw him.
  • How I might avoid making this mistake in the future: It's hard to say.
• 2018.11 - I was on a conference call with a sales rep for the app-development software "Mendix", and I asked the Mendix person why customers create Desktop apps (meaning downloadable software) rather than web apps, and he revealed that the software is not actually capable of creating downloadable / offline desktop apps; by "desktop" they were referring to the software being used in the browser as a web app.
  • This was obviously a minor error on my part.  It seems like the easiest-to-implement fix would be to just always hedge myself by saying "It seems to me that..." or "I got the impression that...".  It seems that many people in everyday conversation are somewhat flexible about interpreting each other's statements, so that "It is the case that..." may be interpreted as "It seems to me that it is the case that...".
  • It may also have been a result of me understanding "desktop" as referring to downloadable software, when they were using it to refer to a web app.  If someone else means something different from what I understand by a term, and I have no reason to suspect that they mean something different, then it seems unavoidable that I may make some kind of mistake based on my understanding of what they meant.