Stealing a piece while the opponent's not looking at the board

Eseles, I would have told him "game over, you lose for cheating, and no more games today".

Maybe I'd play again another time, but maybe not, as nobody likes playing with cheaters.

great idea if one could do it on chess.com to someone with a very short term memory...anyone know how? or who?

On our local club we have a player who is notorious for tricks like illegal moves and such. If he somehow expresses that he made a blunder you must be extra alert, the pawn or piece you can grab is usually poisoned then! Once you know he plays this trick you can use it to your advantage of course. He also lets his playing hand hang over the pieces all the time, as if he is about to move, but then changes his mind and does the same elsewhere on the board...

One time we played a (rated) rapid game and, at some point, he probably knocked one of his rooks off the board with his sleeve. Several moves later (I think it was) he said "hey my rook fell of the board" and puts it back to where it probably was before it fell off. It was under severe time pressure and, although I was sure didn't have a bad position before his rook fell off, I was in a terrible position after he put it back. He of course wanted to continue the game from that point, but I obviously dind't like it at all. We finally agreed to a draw.

I wonder though if you must allow your opponent to put back a piece of which you don't know how and when exactly it fell of the board?

Touching a piece, Is it a required king move ?