We'll start with acronyms that are common to forums. While these have obvious well known meanings, it's the subtle usage behind them that tends to trip people up. I'll try my best to explain.
LOL-Laugh out loud. The poster thought something was slightly humorous. This can also be added to nearly every post on every forum. The post doesn't have to be funny. By doing this, the poster has the option of saying it was "just a joke" and you have no right to get offended by such frivolity.
JK-Just kidding. The poster knows that what he said will be taken as offensive, which he intended, but wants to remove any option for someone else to call him out because of it.
LMAO-Laugh my (expletive deleted) off. The poster is responding to something that was mildly amusing.
ROFL-Roll on the floor laughing. The poster is responding so something that may have actually caused him to smile. Note, this may be followed by modifiers such as MAO, MFAO, MMFAO. These stand for My (expletive deleted) off. My (expletive deleted)(expletive deleted) off, and My mother (expletive deleted)(expletive deleted) off. I'll let you figure out what the expletives are.
IMO-In my opinion. The poster is saying that this is his opinion and if you don't agree with him you are an uneducated dolt who had no right taking up valuable oxygen that could better be used by him.
IMHO-In my honest opinion. Same as above, but by adding "honest" the poster is trying to prevent anyone from calling his own integrity into question.
Now let's move on to some of the guidelines.
-Always assume you are smarter than everybody else posting on a particular forum. Confidence is key to survival.
-No matter what you post, somebody else will have an issue with it. If you posted that you think puppies are cute; you will receive no less than 173 individual responses telling you how and why you are wrong, the Cat Fanciers Association will accuse you of intolerance towards felines, and Pat Robertson will bash you for having a latent fetish for animals.
-Those that don't respond in the above fashion don't even care about what you posted. They are just looking for a thread to "jack" so they can push their own thoughts, products, etc.
-Never bother to read all previous responses to a post. That way, your reply that shows up on page 18 of the responses will be the eleventh such post and everyone will know that you are mainstream.
-Punctuation, spelling, and grammar don't matter. Everyone else loves the challenge of trying to figure out whether you are saying "It's time to eat, Grandma." or "It's time to eat Grandma."
-Threaten those who disagree with you. Online fighting is awesome. When the clear winner is decided, you will be able parade victorious through your mother's basement, re-enacting the epic final battle between Luke Skywalker and Darth Vader with the vintage Light Saber you won on eBay last year.
This list is by no means comprehensive. But hopefully I will help at least someone avoid the trials and tribulations I went through learning all this on my own.
Another noob resource
Because we could all use a little more etiquette.
Something we all can laugh at...well, anyone like me will laugh.
