Hey Lady E,
Writing etiquette is something that seems to have taken a little bit of a back seat in recent years.
Some of the forums and chat rooms will still have people that remember the big push towards "netiquette" from the mid 90's where academics tried to instil the same standards of writing that you would use in a letter to be carried over in to email and web pages.
It is nothing more sinister than this but writing in capitals signifies that you are shouting which is probably why people are getting annoyed with you.
The only other thing to avoid really is too many abbreviations and especially "text speak" (m8 for mate, l8tr for later etc).
If you write as if you were aiming to communicate for the first time with someone (which you probably are) then you shouldn't go far wrong.
hope this was of use and best of luck staying out of trouble.
PS... Don't forget that people tend to be far more outspoken online than they ever would be if meeting face to face or even over the telephone. For some reason people believe that the anonymity that the internet offers gives them an excuse to be rude an aggressive. Sometimes you will just have to accept the fact that you can't please all of the people all of the time.