Disclaimer: For the purposes of fun, and so no one out there think I am picking on them or their fight (because I am not) we will imagine that Fluffy and Fido are fighting about whether or not unicorns. I have no official stance on unicorns.
1. Don't call names. We all joke about using I statements and the like (or is that just my friends), but if you call someone names, instead of discussing the issue you have taken it to a new level and bad things will happen.
So, if Fluffy calls Fido a big, stupid, fizzy idiot, it does not help the discussion. Even if (especially if he does it in the middle of a brilliant point.)
2. Just because someone else started name-calling does not make it okay for you to do it too.
So now that Fluffy called Fido a fizzy idiot, it is not okay for her to call Fluffy a stupid dumbhead.
3. Telling someone they must lead a sad life or not get enough sex or [insert unnecessary judgement about their life here] is really the same as name calling.
So, it is not a good idea for Fluffy to respond by saying, "Wow, I'm sorry you are such a lonely person that worrying about unicorns is such a big deal to you." It adds nothing to the discussion.
4. Things that seem funny in your head, or even when you're sitting on a couch with a friend, often do not come across as funny when done in public, be that in person or on the internet. Read carefully.
So, if Fluffy and Fido always call each other idiot and dumbhead but Sparkles overhears and gets upset that they are being mean, things also might escalate unnecessarily.
5. Telling people to calm down rarely works. More often it is seen as patronizing - you telling them that they are taking it too seriously.
So if Fido says, "Geeze, Sparkles, unicorns aren't that big a deal anyway," - again that helps nothing. Most likely it just ticks Sparkles off more.
6. Don't answer or respond just to respond. That almost always lead to saying things you haven't thought through well. (I know, that one's really hard.)
So, if Sparkles says, "Yes they are!" That's not useful. If Sparkles doesn't have anything new to say, it - hard as it is - is better to say nothing.
7. And sometimes, no matter how well you explain your position, people will still disagree with you. It's weird and shocking and strange, yet true. Continuing to explain the same thing with the same exact words, will not change their mind.
So, Fido might have all sorts of evidence gathered and Sparkles might still not believe Fido. Sometimes that's just the way it goes. Trying to change that makes Fido and Sparkles unhappy, and really the longer the discussion goes on, the less likely it is that either Sparkles or Fido will change their mind.