Berating others
A good player will never tell another player that they are playing badly. Quite the opposite - they might try to make his opponent feel good about playing incorrectly - it's in their best interest! So, if you ever hear someone berating another player, you can be sure that they are a bad player trying to make themselves look better in their peers eyes. That's like admitting out loud - I'm a bad player but I'm trying to convince you that I'm not!
Ellie Biessek
Avoid slow-rolling
Don't confuse it with slow playing - which is pretending that you don't have a good hand while the hand is still in progress to get more money from your opponent on later streets. But once in a showdown and you know you have the best hand then you should show it first. If you wait until your opponent shows their cards or if in any verbal way you make them think that they have won, that's slow-rolling. I have seen some people do this thinking it is funny - but it is a sure way to make instant enemies on every seat around the table plus it's likely to make you the object of gossip for a very long time.
Personal hygiene
If you ever sat next to a person with the personal bouquet strong enough to make your eyes water, you will know what I'm talking about. Please don't use a strategy of 'a skunk' to make sure that your opponent can't concentrate and take a shower at least 24 hours before entering a poker room.
Stalling the game
Poker is a social game and many people are there for fun. If you are talking to a friend, watching a video on your iPad, or texting a friend (not advisable by the way), make sure that at least you know when it's your turn. Someone who constantly needs to be reminded to act, or who forgets to put in their ante because they're not concentrating, shouldn't be playing at all. Also, I have seen players pretending that they have a tough decision, even pre-flop, on every hand they play. That's just wasting everybody's time.
Attacking the Dealer
Let's face the truth - the occupation of the person who is dealing the cards is a 'dealer' not 'magician'. They have absolutely no control over the cards they give you and, if they did, I can assure you they would make much better money else were. Don't be one of those bad losers who likes to blame other people for their losses. It's also worth noting that throwing cards at the dealer will most likely get you banned from a casino.
Calling the clock
The option of calling the clock is the right of every poker player but overdoing it, or not being considerate, can upset other players. If you see a player genuinely thinking over a hand, especially when they don't normally take this long, try to give them as much time as you would like to be given in the situation. On the other hand, generally other players will give you more time if you really are taking time out to think. In my experience, talking to others while everybody is waiting for you to make a decision will make someone put a clock on you much quicker.