QH5

e4  e5

Qh5

So everyone says that this is a mistake. Can someone prove to me why it is wrong?

You lose lots, and lots, and lots of tempi. :P

I think you mean "2. Qh5!!", because this is white's best move ever.

Or at least that's what someone tried telling me the other day.  His reasoning was even more rediculous than the move itself, hehe.

The main idea is to to play Qxe5 mate(!!), as long as Black feels like taking his King for a walk on move 2.

That's why it is known as the anti-counter-bongcloud defence attack.

Can you tell us what his reasoning was? I'd like to hear it.

It is not a mistake, but it is definitely not the best move.

Qh5 is mostly played by beginners and low rated players(with few notable exceptions) hoping to take an opponents rook or to achieve a Schollars mate.

It can win you some games against an unprepared/unskilled opponent, especially in blitz play, but it is not a best opening out-there.

As already pointed out by PawnAvalanche, if black knows what to play, after several moves he will have a lead in development, and white will have an awkwardly placed queen which also takes the best spot for white knight.

I'd go as far as call it a mistake. I don't have any games in my own archives to show you because I play the Sicilian as black, but all the games where my opponent moved his queen out on the second move I classified in the "slaughter" folder. Granted, it means by default that my opponent was a bad player, but what usually happens is that I end up trapping their queen somehow.

because your opening must develop your pieces to give checkmate in the endgame but early development of your queen like that is pointless and lets the black player develop his pieces earlier than you which is bad for you 

the white player starts (opens) and the black player defends thats why black openings are commonly defenses

Most probably because the queen will be useless if black defends f7 and e5.

As I said, IMO not a mistake, but not the best move either.

There is a reason for it to be called (among other names) "patzer opening" 

http://en.wikipedia.org/wiki/Parham_Attack

http://www.365chess.com/opening.php?m=4&n=332&ms=e4.e5.Qh5&ns=3.5.332

If you are playing someone you have no chance of legitimately beating or even drawing (say, if I were playing Anand), it is the best move. Why? Your opponent might accidentally brush the king with his hand, thereby causing him to be forced to play 2... Ke7 thanks to touch move, and falling to 3. Qxe5#. It might be long odds, but much shorter odds than beating them with skill :P

Just for means of illustration, here is a typical continuation after Qh5. There are some ways to vary, but while black has a small advantage, this structure is very easy to play for white.

it's a bad move because after Nc6 next move black will kick the queen and then you loose tempo

Sorry, what's so passive about d6? It will be played anyway sooner or later since d5 is not possible, and it frees up the bishop (also threatening Bg4). I don't see any other great moves here, Bh6 is interesting, but white will still untangle his position.

Of course, perhaps 5. c3 isn't the best move. 5. Ne2 is probably stronger.

@ shoopi

1.e4 e5 2.Qh5 Nc6 3.Bc4 g6 4.Qf3 Nf6 5.c3?

5.c3 is not book.

5.c3 swings the evaluation too far in Black's favor, thus you don't see it played. Black would punish White with either 5...Be7, 5...Bh6 or 5...Na5.

Black already has an advantage after 4...Nf6, so I don't know why Nakamura bothered with 2.Qh5 at all in a few games a couple of years ago. I've only found one game in a 4.5 million game database where Nakamura won with this opening. The rest he lost or drawn. 

Here's an example with two pros playing a book line with 2.Qh5.

The touch move rule only applies to deliberate touches of the pieces, not accidental touches.

Well, if he didn't say „j’adoube“ (Article 4.2. FIDE laws of chess) he may end up having to play Ke7(Article 4.3.) , depending on a arbiter's opinion.

What is "deliberate" can be subject of opinion.

I would like to know more about the real situations that occurred in tournament practice and their outcome, but this would probably be more appropriate to be started in another thread(maybe there is one already).

EDIT: I have found some interesting threads about "touch rule".

http://www.chess.com/forum/view/fun-with-chess/touch-move-rule-misuse

http://www.chess.com/forum/view/general/rules-clarifications?quote_id=4020416

waste of a tempo