There are many ways to approximate an appropriate level of civility and a forum that has once aggressively enforced the "don't be stupid in D&D or we'll bite you" rule should have no problems with identifying generally uncivil behavior. For specifics we can ask ourselves questions such as, "Am I trying to be a smartass? Am I trying to corner my opponent? Am I trying to cast his posts as being absurd? Am I acting as if he's crazy, stupid or corrupt? Am I using bad language? Am I using

and

? Am I trying to make my opponent feel small and inadequate? Am I trying to shame my opponent for holding a view I disagree with? Am I treating the subject as being more important than the person?" and so on and so forth. If you disagree with some of my examples I have no doubt you can find better ones, because there are plenty.
We're grown-ups. I usually know when I'm being a dick. You usually know when you're being a dick. Our problem isn't that we don't recognise when we're being uncivil or dickish or crossing boundaries--it's that we recognise it but do it
anyway. When it's pointed out to us by others we do our best to justify it. When we inadvertently step on someone's feelings it either doesn't come to light because we act as if feeling stepped on isn't legitimate, or, if it does come to light, we explain it away and insist that the person in question submit and grow a thicker skin;
as if having to say "Sorry, that wasn't my intention," or to accept an apology or to accept someone else's feelings of offense as being valid or to give someone more chances to save face by asking for clarification or giving things a second go or even just letting things go constitutes unacceptable restrictions of freedom that would make this place no better than the last days of Atari. Worst of all, we don't even encourage each other when we
aren't openly fighting.
That is how I'd characterise the problematic aspects of this forum. Would you say I'm very far off the mark? I sincerely doubt that things are the way they are because Dread twiddles his thumbs all day long and shirks his modsticking duties.