Knife licker.
I think people who enter into marriage with a true spirit of compromise and a desire to make it work will be WILLING to change (to a point) for their spouse. For example, I think an improvement in table manners would just naturally occur over time - it's an easy compromise to make in order to bring your wife peace of mind.
But if you marry a compulsive cheater, for example...chances are, that isn't going to change. An alcoholic...a wife beater, a liar, a thief...those things don't just magically go away upon getting married. And nobody ever strengthened a relationship by continually carping on something, so it's best just not to marry people who have characteristics you want to go away.