I just saw this from an old posting from MarkPilgrim's DiveIntoMark. This beautifully summarizes what it is I get pissed off about when talking to people online. It's when they are logically rude. I don't mind being told I'm wrong, I don't mind being yelled at ... what pisses me off more than anything else is when people are logically rude.
In college, I was a philosophy major, and I had a wonderful philosophy professor who wrote a wonderful article called Logical Rudeness. Philosophy is all about conversation, especially (in the last few hundred years) written conversation. One philosopher comes up with an idea and writes it down and publishes it. Other philosophers pick it apart, look for hidden assumptions, look for leaps in logic, deny axioms, argue conclusions, split hairs, go every which way with it. This is logically polite. It adds to the conversation, the ongoing argument. The arguments run deep, and in ten thousand years they have not been resolved, nor will they be resolved in the next ten thousand years. That is irrelevant. The essence of philosophy is not the conclusion but the conversation. But along the way, and increasingly in modern times, there are a few philosophers who actively attack this conversation. There are philosophical systems which preclude further argument. If, for instance, you believe that thinking itself is a disease that must be cured, no philosophical argument can sway you. The act of making the argument, by definition, involves thinking, so it is simply giving further proof that the person making the argument is diseased. (Im not making this up; there are philosophers who believe this.) This is logically rude, not simply because it is impervious to logic (although it is), but because it is a philosophy which denies other philosophers the chance to philosophize in return. It stops the conversation.
Note that this is different, in an important way, from a philosopher (like, say, Kant) who believes that he has it all figured out and builds a comprehensive philosophical system to try to stomp on other philosophical systems. Lots of later philosophers argued with Kant; some accepted his premises and went in a different direction, others rejected his basic premises altogether. But as comprehensive as Kants system was, there was nothing in it that precluded arguing against it. Kant savaged all philosophers who had come before him, but in the end, he was logically polite. He added to the conversation, steered it in a new direction... but then the conversation continued.
Source: http://diveintomark.org/archives/2001/10/01.html#write