[rminusq]

Since this is in MTT Community, I'll trust that you're asking about in a live tournament, and answer with my understanding for that situation.

[ QUOTE ]
Imagine you're HU and you speak out of turn, by showing your cards. In that case your hand is not dead because you're HU and it's show down anyway. The person that was supposed to act first has the right to much or to show. But the cards are not dead. So far so good.

[/ QUOTE ]
You mean after all action is complete? Of course you can show your hand in any order. If there is still action, the hand is heads-up, but the tournament is not, you should not show your hand (debate rages about this, but present practice is it's not allowed most of the time). Your hand wouldn't be called dead, but you might receive a penalty afterwards.

[ QUOTE ]
What happens if you're in the middle of the game in a multi way pot and you suddenly drop your cards because you're an idiot and one card ends face up on the table. If this is my home game I would allow the guy to continue but the card shows must be visible to all players.

[/ QUOTE ]
Sounds about right. If anyone sees a card, everyone in the hand is entitled to see it.

[ QUOTE ]
Another situation: Imagine you're in a multi way pot and you decide to show one card to get a read. Cards dead or not?

[/ QUOTE ]
Don't do it. In a multi-way tournament, or a multi-hand cash game, just don't [censored] do it. As I said, most places it's against the rules, and it's probably not going to give you any more useful information. Again, in a tournament, hand wouldn't be dead (most likely), but penalties might be enforced. In a cash game, in some casinos, your hand would be dead, and other people would be pissed at you.

For instance, say the board is 8s 5s 2s Ah. You check, Player B bets, Player C raises, and you decide to flash your As to see if you can get a read that chasing your flush draw is worth it. Eventually you decide to fold. Now Player B knows his Ks 4s is the stone-cold, and Player C with his Qs 7s can't pretend to have the ace anymore. You've just screwed Player C, and he will have every right to give you a kick in the nuts.