Usually when I hear the word “etiquette”, what comes to mind is a white-gloved Ann Landers sitting straight-backed creating her daily newspaper column by way of an old fashioned, manual typewriter. 
Then, you add the word “poker”, and Ann’s image instantly morphs into the Dogs Playing Poker painting by C. M. Coolidge. Go figure… I have a vivid imagination.
Typically, the word etiquette means "rules of acceptable behavior: the rules and conventions governing correct or polite behavior in society in general or in a specific social or professional group or situation.” (Thank you, MSN Encarta dictionary.)
While we're not talking about a white-gloved ceremony, (not really my specialty, as you might imagine), let's just say there are similarities between the ceremony and etiquette of poker games and what you learned in kindergarten. Did that just take the wind out of your sails?
Okay, when we talk about poker etiquette, we're talking about agreed-upon ways of acting at the poker table. So, take what you learned in pre-school and combine that with the rules created by the Tournament Directors Association (TDA). Even when you are playing in a cash game, these poker tournament rules will serve you well.
TDA rules are personal to me. Even thought I was not one of the founders of the Tournament Directors Association, I was intimately involved with the tedious creation of the rules earlier in this century. (Don’t wise crack.) It involved thousands of emails over nearly a year, and, yes, I am as protective as a she lion of her cubs.
Why should you care about poker etiquette? You paid your money to play, you are a rebel, or, you are frankly not concerned with convention in general. Besides, you turned to poker as a diversion from all the constraints put on you in your daily life. Right?
You should care because unless you know how to act at the poker table, you might be given a penalty “time out”, or, your hand could be ruled dead, causing you to lose a pot you might have won. It might have been that one significant pot that would have made the difference between you actually winning the entire poker tournament or busting out before reaching a payday.
Besides, would you rather learn how to act at the poker table or risk being stoned by the other players? It’s not a popularity contest, but it is about having fun while you turn a profit.