Here's one...
In a game last week a player went all in. He was called by one other player and others folded round to me. I was the last to act. I was holding ace nine unsuited and was considering calling. As it made no difference if my cards were seen, I turned them over so all could see my dilemma. I then folded straight away, as had been my intention when I turned the cards.
The problem was, one of the all in players also has ace nine unsuited and had a right go at me for "ruining his chances". I pointed out that whether he saw my cards or not would not have any effect on the hand, but he got all pissy, saying what I had done breached "poker etiquette". Of course, he lost to a pocket pair and went out in a huff.
Was what I did wrong? I didn't influence the outcome of the game or anyones betting. I've seen other people do it and it never bothers me. If it scuppered my own chances of winning an all in by them having some of the cards I wanted I would just accept it, not have a go. After all, seeing them doesn't change a thing, except you are now aware that your odds of winning are shortened.
In addition, is it proper to state what hand you have when betting is still going on, either to bluff by lying or double bluff by telling the truth?