The unsoundest opening that you've ever lost a game to

wow so many unheard of openings....

Here is a game which will always fascinate me. A player with roughly master strength ignores all the opening principles:

1.a3 is sometimes referred to as the Anderssen Opening, because Adolf Anderssen played it against Paul Morphy a few times during their match.

Well I've lost to the Delayed exchange (double deffered?) variation of the Ruy Lopez at least twice now.  That's pretty frustrating.  Umm... lost to the haloween gambit a couple times. ... otherwise most of my 'unsound' losses come from blitz games, which kinda doesn't count :P.

I once lost to an unsound piece sacrifice on move 4

Playing 1.e4 I have lost to 1...f5 in blitz, not sure what it is called but it is crap. I have also lost to the grob, which I actually don't consider totally bad. I have lost to the elephant gambit multiple times, especially in blitz. I hate it how my queen blocks in my king's bishop in the main line (or what I think is the main line) of it.

I think this gambit doesn't work...

1.e4 f5 is apparently known as the Duras Gambit or the Fred Gambit.  Oldrich Duras was a strong player in the early years of the 20th century, but I don't think he ever played it against a strong master.

Try not to laugh too hard at this one ...

Damiano's Defence 1.e4 e5 2.Nf3 f6?! is regarded as unsound, and 3.Nxe5 is often given as one possible refutation.  Stronger is 2...Nc6 leading to a Ruy Lopez or 2...Nf6 the Petroff.

I once lost to 1.f3 e5 2.kf2 d5    that was painful....

I lost my first rated game here on chess.com to a scholars mate!! That was extremely painful, and although coming back from a queen down to win my first actual game (against my "greeter") did provide some solace, it didn't help my rating any...

A good friend of mine played nothing but the Grob for almost a year - yes, as white and black. So I must have lost to that a few dozen odd times...

I lost a game against the Damiano, after the moves 1. e4 e5 2. Nf3 f6 3. Nxe4 fxe4 4. Qh5 g6 5. Qxe5+ Qe7 6. Qxh8 Qxe4+ 7. Kd1.

It was a terribly embarrassing loss. I was up a rook, but ended up with my queen locked away in the corner, as I spent too much time developing and not enough time looking after my committed Excellency.

In the Damiano, I once allowed a draw after 1.e4 e5 2.Nf3 f6 3.Nxe5 Qe7, so I ended up switching to 3.d4.  Not as violent, but I've chalked up five wins so far.

I bet a 2100 rated on RHP that I could beat him if he played 1.a4 & 2.h4.

I resigned on move 38.

In college, I may have lost a game or two to what we called the Meatball.

1.e4 f5 2.exf5 Kf7

2...Ng8 is not unsound. It's fine. I'm suprised someone like you would think it is.

In a 1 minute game I lost as black to 1 g4 d5 2 g5 Qxg5 3 a3 e5 4 d4 exd4 5 Bxg5, and resigned.

Lol Ng8 IS in fact unsound :P.  You'll never see it played at master level... ever.

Petrosian played it once in a training game with Boleslavsky in 1966, but he ended up losing.  Indian GM Chanda Sandipan also tried it once, but he also lost.  In Gonnosuke's case though, I think it's more that he'd rather sac the piece than retreat it.

I think black can try to chip away at those pawns, and he hasn't commited to ...e6 like in the french. Now black lost many tempos of course but I'm sure he's ok as he's not so much behind in development but in pawn moves, like the regular alekhine. And a move like that would have much suprise value. It can't be too bad since in the regular ...Nd5 alekhine it's not like black's knight is ultra useful on b6 since it just attacks c4. If black is apparently ok when white advanced 4 pawns, what's so bad about 2 or 3? Fritz doesn't seem to hate it, though white gets the edge. It's one of those openings where concrete analysis is important not just black's ideas because I guess there are some sharp things white can do.