1)  Never make a personal attack.

2)  Always reread the entire post before submitting.  Besides letting me fix typos and rearrange things to ensure clarity, I can also check to make sure I did not violate rule #1, even accidently via a possible misinterpretation.

They are very similar to some of Leo's rules.

On the web I find it best to avoid using sarcasm.  IRL I love sarcasm and like to tease friends and family using it.  However I find that it is hard to pull off on the web due to the lack of tone.  Thus I very rarely use it.  When I do use it, it is always of a joking manor and not as part of an argument or debate.  Even then I will only do it if it can easily be identified as sarcasm and I know the target well enough to know that they will not be offended and realize I am teasing them.  While I do not think sarcasm should be against the rules, I think people should use it with caution.  It is also usually counterproductive in a friendly debate

pejorative: having negative connotations; especially : tending to disparage or belittle

If pejorative language is directed at a participent in the debate, then yes, by definition it is a personal attack and should be avoided.  If it is directed towards the subject of the debate, a war, a religion, a country, a leader, etc...  then I think it is acceptable.  If hearing such language directed towards something they hold dear will cause someone extreme hurt or anger, than perhaps it is best that they avoid the P&R area.

As a rule I try to avoid labeling someone during a debate or calling them a name, even one I think would not offend them.  I may however let them know what I think of their views.  I might say for example, "What you said sounds similar to Communism?"  It may only be semantics, but the way you phrase things can make a big difference.  I think "You must be a Communist to think that way." might seem like a personal attack to some and "What you said sounds similar to Communism?" is a valid point in a debate.  This is why I often reread my post several times and make alot of grammer and phrasing changes.  I also try to keep in mind that many posters to this board have English as a second language.  So I avoid using idioms and phrases that may be easy to misinterpret as much as possible.  My training and experience as an English teacher in Japan gives me an advantage there.  Also the fact that my wife is not a native English speaker helps a lot as well.

Some pet peves of mine that bug me from other posters are when certain opinions are presented as facts or when a fact is presented (which is not well known; saying the earth is round wouldn't qualify for example) and no documentation (via a link or at least a source) is given.  I try very hard to stick to this rule (though I'm sure I've broken it on occasion) and often I have had to just abandon a line of thought because I couldn't find anything to back it up with or something which I thought was damning evidence turns out to just be wishy washy at best. 

Stick to the subject.  I realize we go on tangents and that's fine but don't derail an interesting thread.

This particularly bugs me since it stops cold the discussion and I think actually puts the person on the spot when they don't necessarilly deserve it.  It also attacks the intellegence of the person and puts it out in public.  It's one thing if you're in school and your teacher does things like this but it's a totally different thing when you're having a discussion about a subject and someone jumps in and points out that you mispelled a word.  It's like if you're watching a debate and one guy says to the other, "your zipper's down," on live T.V.  If you're annoyed with someone's grammar or spelling, pm them.  Don't make it a public spectacle.  If you're joking around with someone though, that's different but I think in the P&R forum, it should just not be done.