The Internet is a kind of a foreign country, so you have to respect its customs. These rules are really important for all us. There are many documents around talking about this subject, so please consider this page just as a set of guidelines. There are different rules according to the ambit in which you are acting. So there are rules concerning Email, Newsgroups, FTP, Telnet, IRC and so on.
Flames are real wars usually burst in consequence of a misunderstood.
In fact misunderstanding is extremely easy on the net, because you can't see your interlocutor. For this reason someone invented 'smiles'. So beware of sarcasm. I think you should think two times before reacting to a presumed affront. Smiles are very helpful here, because they 'show' your real mood.