Etiquette On and Off the Poker Table

Playing poker online can teach you all the rules you need to know to play the game - and how to win at it. But it will teach you none of the necessary etiquette for playing live.
Although as a beginner your primary concern may be how to maximize your winnings, it's actually important to familiarize yourself with poker etiquette. Mutual respect is crucial in poker, and the game has its own formalized system of dos and don'ts.
Asking to See a Losing Hand
First off, you never ask to see another player's losing hand. Yes; you're allowed to ask to see any hand called on the river. And yes; by doing so you glean a lot of information as to what the other infrared contactlenses player was playing. That is not reason enough to make the faux pas.
The reason you are allowed to request to see a called hand is to help thwart any players' attempts at collaboration. If you ask to see a player's hand, even with the intention of seeing what they're playing, you are technically accusing them of cheating.
Not only that, you're needling the person, forcing them to show the table their losing hand and expose any mistakes they may have made. It's a disrespectful thing to do, and in a private game you would be asked to leave for doing it.
Knocking Someone Out of a Tourney
When you knock someone out of a tourney, or cash game, it's up to them to shake your hand. Never offer to shake their hand; it puts them in a bad spot. Even though you're trying to be friendly, think about it from their point of view: when you get knocked out of something, you're usually pretty pissed off.
Most people don't want to shake someone's hand at that point. By offering, you are making them do something they don't want to do, or look like a huge jerk by refusing.
Don't Apologize
Never apologize when you win a hand. You came to the table to win people's money. How you do it doesn't matter. By apologizing for taking someone's money, you're simply lying to them. You're not sorry you hit your one-outer; in fact you're relieved. No one appreciates being lied to. Just say nice hand and move on.
If You're Not in the Hand, Stay Out of the Hand
When a player asks someone else a question, leave it to that player to answer. The reasons players pose questions such as "How many chips do you have left?" rarely have anything to do with wanting to know the answer to the question.
Most strong poker marked cards players can consistently eyeball stack size within a very small margin of error. Questions put to other players are usually done so as to try and pick up tells. If some other idiot answers for the player on the table, it messes up the whole plan.
Advantage Play
Advantage play is a grey area. Advantage play is using any information you should not have to assist you in the hand. The way I split it up, if you see someone's card because of something the dealer did, you should speak up and call it a flash card.
If you see someone's hand because of his own actions, then it's free game. If the way I look at my cards gives you a view of my hand, then that's my mistake and I will not fault you for using that knowledge to your own advantage. But I don't feel people should be penalized as a result of an incompetent dealer.
It may seem questionable to look at someone else's hand, but as Canada Bill Jones once said, "It's immoral to let a sucker keep his money."
Conclusion
All these etiquette rules were designed and put into place to keep the game running smoothly and with a healthy amount of respect. In the olden days, these were the unspoken rules that kept you from getting shot at the table.