mean as a snake

Mean as a snake is an expression used for someone who is mean in the sneaky and treacherous way. This person might not be as outward and blunt about their meanness such as being rude to your face, but they are mean in the sneaky way through lies and deceit and various types of treachery. Like a snack in the grass that sneaks around attacking their pry, a person who is mean as a snake acts in much the same way.