John Scalzi at Whatever asks 10 useful questions we should all be asking ourselves about our commenting habits. These two points made in his answers to those questions stood out strongly as things I keep on running into all the time, including offline.
4. If I’m making an argument, do I actually know how to make an argument?
[...]in my experience the single most common bad argument is the assumption that one’s personal experience is universal rather than intensely personal and anecdotal. Sorry, folks: you are probably not actually the living avatar of What Everyone Believes and Knows.
Secondly: in the answer to his sixth question he links to a classic post of his from 2010 which led to many t-shirts:
This is a continuing feature of your average night of stand-up comedy, and I’ve been guilty of it more than once myself while blogging and also in my offline banter. Apart from the quip often falling flat purely as a performance, in person it’s simply rude.
Finally, this is the one I think I most need to remember Elsewhere especially:
10. Do I know when I’m done? I’m not saying you should enter each comment thread with an exit strategy, but on the other hand, it wouldn’t hurt. It’s okay not to make a lifetime commitment to a comment thread. Likewise: If you’re having a conversation in a comment thread that’s going nowhere, it’s okay to admit it and get out. Letting the other dude have the last word will not mean you have Lost the Internets; really, quite the opposite, in fact. Similarly, if you find a comment thread is making you angry or sick or pissed off, walk away. If you find that the reason you’re still in a comment thread is to thump on someone else, go get some air. If the thread has stopped being fun and started to be something like work, seriously, man, what the hell are you doing? Go away. It’s a comment thread.