I remember hearing once at a melaveh malka a story:
Once a visitor came knocking at the door of a guy who had saved up a small fortune. He said to the woman who came to the door, “your husband requested that you give me the money” The wife obviously refused. So the the visitor said “your husband gave me a sign that you should believe me, you had such and such for dinner (meatballs and spaghetti?) So the wife believed him and handed over the money. The husband came home, and the wife told him that she gave the money as he requested. The husband flew into a rage and killed his wife. The thief had seen the remnants of the meal on the husbands face, and used the information to trick the wife.
Therefore, men wash mayim achronim.