Pelching (or to pelch) is an unfortunate side affect of people who have failed to mature mentally. It is the act of trying to reverse actions taken in a game done by one who cannot fathom the concepts of losing or fair play.
Sylvia: Knight to queen's rook.
Andy: Hey, I didn't see that or I wouldn't have moved my pawn. Give me back by rook.
Sylvia: Hey, no pelching!