Same as what's considered rude in REAL LIFE. With the additions or clarifications in http://www.answerbag.com/a_view/2227769 .

1. Someone farting in the restaurant when I am enjoying my steak. 2. Someone puking when I am studying. 3. Someone watching the show,"Do-Ray-Mee"(Lol)

Retaliatory down rating--that's when you down rate another user because you know/think they down rated you. Accusing other users of down rating you--we can't know who down rates us unless they admit to it. Using vulgar, profane, or obscene language--Using * or @#$#$# in place of these words is just as effective as the actual words. It's really better to just avoid that kind of language, if possible. Avoiding profanity makes your argument more effective, anyway. "Coming on" to users you barely know--this makes us uncomfortable. Make sure you know if that person is open to that sort of thing before hand or you'll creep him/her out. Taking your argument across threads--This means you take an argument you were having on one comment thread and find the other party or parties and start your argument up again where it doesn't belong. This usually gets innocent parties, who would probably rather avoid that sort of thing, involved. Asking questions that name or ask us to name other users--A lot of people are not comfortable in the lime light and would rather keep their names off the home page. Asking congratulatory questions without the congratulatoree's permission--the person who is being congratulated may want a friend to ask or may not want a question in the first place.

the fact that i just downrated you for no reason is kinda rude.

I think Idne has covered most of it . Typing in Capitals is also considered rude it is the Internet s equivilent of shouting. Deliberately misunderstanding something a person has said for the sake of spite and drama. Using that dramatic streak to try to give another user a hard time.