In the above position, that arose from a King's Gambit Accepted, white has an edge. The pawn will be recovered, when the bishop pair and open lines will give an advantage. The black knight on c6 is also somewhat offside. Can you find the very bad plan that black found very quickly? and white's reply? No prize or bragging rights for finding the losing moves!

... O-O-O followed by Bh3?

plan Bxd4  cxd4   Nxd4 threaten Queen and move to c2+ next forking King and Rook?

Wish I could have seen absurd's before submiting 

Surely the attractive O-O-O?? followed by Bh3. Absurd has it first.

The winning move caused my opponent (rated 1760) to resign immediately, the blood draining from his face. A rare pleasure, on what I expected to be a very long afternoon. Happy days!

Yes! 0-0-0 (intending to skewer my Queen to my King after Nxe4 dxe4 Qxe4 Rde8) but after Bh3 finding his own Queen pinned. Oh! the sweet irony.

I'm pretty sure the blood draining from his face had more to do with your fangs in his neck than the move... haha.

yikes!!!! 0-0-0 would be the worst move ever!!!!

Qe7?

haha, so easy to blunder when castling.  Another good one when castling queenside is getting your rooks forked.