Ok, I'll try to explain is really fast:
1) Player A enters the game.
2) PLayer B enters the game, and doesn't touch a damn thing. Don't touch your mouse pad or keyboard or even come close to yourr computer after you presss "Join Game"
3) Player A does his thing... Cube, sockets, whatever.
4) If he doesn't like the outcome, he goes up to Player B, and clicks on him, as if he wanted to trade with him.
5) Player B then presses Alt+F4, causing his Diablo screen to crash completely, and this also causes the game the drop.
That is it. Once the game drops and PLayer B gets booted off Bnet, all your items are back the way they wer before. THe only side effect is that Player B will have a RD for about 5-10 minutes...
Trust me, it works. Ask Doofus, me and him have crafted a shit load of 11 life leech rings dong this technique.
Good luck, and have fun!