[ mona / prog / sol ]
Everything is already said in RFC 1855 (Netiquette Guidelines) When was it suddenly superseded?
Diversity? Respect? Inclusion? Sexual harassment?
Remember that the recipient is a human being whose culture, language, and humor have different points of reference from your own. Remember that date formats, measurements, and idioms may not travel well. Be especially careful with sarcasm.
There are Newsgroups and Mailing Lists which discuss topics of wide varieties of interests. These represent a diversity of lifestyles, religions, and cultures. Posting articles or sending messages to a group whose point of view is offensive to you simply to tell them they are offensive is not acceptable. Sexually and racially harassing messages may also have legal implications. There is software available to filter items you might find objectionable.
Since the Internet spans the globe, remember that Information Services might reflect culture and life-style markedly different from your own community. Materials you find offensive may originate in a geography which finds them acceptable. Keep an open mind.
Microaggressions? Trigger warnings?
Wait overnight to send emotional responses to messages. If you have really strong feelings about a subject, indicate it via FLAME ON/OFF enclosures. For example: FLAME ON: This type of argument is not worth the bandwidth it takes to send it. It's illogical and poorly reasoned. The rest of the world agrees with me. FLAME OFF
But, of course, people shoving their CoC down everyone's throat weren't even born.